score:4
If the new travel dates fit into your duration and validity period, there is no need to inform the consulate -- business meetings get rescheduled all the time, and that's why most applicants get a few extra days on their visa.
The immigration officers might ask on arrival, simply show them your new travel plans and tickets.
If the new dates exceed either the duration or the validity period, of course you will need a new visa.
Upvote:1
I received the following response from the visa section of the Spanish consulate in Mumbai.
Good morning,
Kindly note as you have been granted a multiple entry visa valid until XX-XX-2020, you may travel as many times on any given days during the validity of the visa. You need not send any notification to the Consulate. However, kindly note permission to enter or denying entry into the territory is the decision of the immigration authorities.
Regards, Jefe de Visado / Visa Officer Secciรณn de Visados/Visa Section
Since this matches the information in @o.m.'s answer, I am accepting it.