Were the islands/countries discovered by Hispanic explorers named after Mozarabic feast days?

Were islands/countries discovered by Hispanic explorers named after Mozarabic feast days?

The short answer is no.

But that no has to be clarified. It could be yes or no, according to which Rite the person who named the said lands belonged to. Both Rites were in use in Spain at the time of the Spanish colonization of the Americas.

The name "Mozarabic Rite" is given to the rite used generally in Spain and in what afterwards became Portugal from the earliest times of which we have any information down to the latter part of the eleventh century, and still surviving in the Capilla Muzárabe in Toledo cathedral and in the chapel of San Salvador or Talavera, in the old cathedral of Salamanca. The name is not a good one. It originated in the fact that, after its abolition in Christian Spain, the rite continued to be used by the Christians in the Moorish dominions who were known as Mazárabes or Muzárabes. The form Mostárabes is also found. The derivation of the word is not quite certain, but the best theory seems to be that it is musta’rab, the participle of the tenth form of the verb ’araba, and that it means a naturalized Arab or one who has adopted Arab customs or nationality, an Arabized person. Some, with less probability, have made it a Latin or Spanish compound, Mixto-Arabic. The meanings, which are not far apart, applied entirely to the persons who used the rite in its later period, and not to the rite itself, which has no sign of any Arab influence. The names Gothic, Toledan, Isidorian, have also been applied to the rite—the first referring to its development during the time of the Visigothic kingdom of Spain, the second to the metropolitan city which was its headquarters, and the third to the idea that it owed, if not its existence, at any rate a considerable revision. - Mozarabic Rite (Catholic Encyclopædia)

It should be noted that none of explorers of the 15th or 16th centuries were sent from the Archdiocese of Braga, Portugal. Braga also had it’s own liturgical Rite within the Church.

The Rite of Braga (or Bragan Rite) is a Catholic liturgical rite associated with the Archdiocese of Braga in Portugal.

The Rite of Braga belongs to the Roman family of liturgical rites and took shape within the Archdiocese of Braga between the 11th and 13th centuries.[1] The Missal of Mateus, which dates to the second quarter of the twelfth century, is the oldest known source for this Rite. It was more than 200 years old at the time of Pope Pius V's papal bulls Quod a nobis of 9 July 1568 and Quo primum of 14 July 1570. The rite was unaffected by the imposition of the Roman Rite throughout the Latin Church. This was due to the exception made for regions where another rite had been in use for at least two centuries. However, the Roman Rite was increasingly adopted within the archdiocese and non-traditional elements were admitted into celebrations of the archdiocese's rite.

In the 20th century an attempt was made by Archbishop Manuel Vieira de Matos, with the approval of Pope Pius XI, to expunge these accretions, to revise the texts and to make the rite obligatory within the archdiocese. After the Second Vatican Council the priests of the archdiocese, while authorized to use the Rite of Braga, have in general opted to use the Roman Rite. The Rite of Braga

The Mozarabic Rite, also called the Visigothic Rite or the Hispanic Rite, is a liturgical rite of the Latin Church once used generally in the Iberian Peninsula (Hispania), in what is now Spain and Portugal. Thus we can call it a liturgical variation of the Extraordinary Form of the Mass.

Since the liturgical reform of Pope St. Paul VI, the Mozarabic Rite has almost completely disappeared within Spain. The Mass according to this liturgical Rite can still be found in Spain if one looks hard enough.

Here is the real conundrum with this question. The feast days of the Tridentine Roman Rite and the Mozarabic Rite for the most part followed the same liturgical calendar with a few minor exceptions. In this sense the naming of the lands discovered in the 15th and 16th centuries could be literally named according to either liturgical Rite. It would all depend on which Rite the person who named the islands belonged to. It is sure that both Rites were in use in Spain at the time.

It should be noted the Spain has (and did have) some local feasts not celebrated in other countries and this also applies (and did apply) to both liturgical Rites.

As I have already stated above that the true answer to this question will depend on which Rite the person of authority belonged to. As it happens, both Queen Isabella of Spain and Christopher Columbus were of the Roman Rite.

Christopher Columbus in fact was Italian and that says volumes to this subject matter:

Christopher Columbus [(before 31 October 1451 – 20 May 1506) was an Italian explorer, navigator, and colonist who completed four voyages across the Atlantic Ocean under the auspices of the Catholic Monarchs of Castile and Aragon. He led the first European expeditions to the Caribbean, Central America, and South America, initiating the permanent European colonization of the Americas. Columbus discovered a viable sailing route to the Americas, a continent that was then unknown to the Old World. While what he thought he had discovered was a route to the Far East, he is credited with the opening of the Americas for conquest and settlement by Europeans. - Christopher Columbus (Wikipedia)

The Catholic Encyclopedia further states that in Queen Isabella’s day the Roman Rite prevailed and that she allowed the Mozarabic Rite to be used within the Spanish Kingdom:

When Ferdinand and Isabella took Granada in 1492, there were certainly some Mozarabic Christians there, as well as Christian merchants and prisoners from non-Moorish countries, but whether the Mozarabic Rite was used by them does not appear. With the discouragement which began with Alfonso VI came the period of decadence. The civil privileges (fueros) of the Toledo Mozárabes, which, though in 1147 Pope Eugene III had definitely put them under the jurisdiction of the bishop of the diocese, included a certain amount of independence, were confirmed by Alfonso VII in 1118, by Peter in 1350, by Henry II in 1379, and by Ferdinand and Isabella in 1480 (later also by Philip II in 1564, by Charles II in 1699, and by Philip V in 1740). But in spite of this the "Roman Rite prevailed so much that it was introduced even into Mozarabic churches, which only used the old rite for certain special days, and that in a corrupted form from old and imperfectly understood manuscripts This and the dying out of many Mozarabic families gradually brought the rite very low. - Mozarabic Rite (Catholic Encyclopedia)