Upvote:5
A 5-year multiple-entry visa is basically the highest possible privilege which can be granted to a Schengen visitor.
It is normally granted after multiple visas of increasing durations or if your circumstances are very favourable.
In short, it means “we trust you, you can come and go as you want”, as long as you continue to meet the conditions of the visa, i.e. the 90/180 rule, no overstaying, no working in Schengen, and so on.
In theory, you are expected to do what you said you would do on your first visit, with minor changes. But:
There is no obligation to use the visa within a given period.
If you want to be absolutely safe you can contact the embassy or consulate which issued your visa and advise them of your change in plans, but I really don’t foresee a problem.