No it is not possible to prevent new hints for a specific individual.

You probably are already aware that in MemberTrees' 'List of People' the hints are now sorted as to type, and you can click to look at Tree Hints and click to "ignore" Tree Hints for any individual you wish right there, without having to go to the Individual Profile page, click on Hints there and click to ignore specific hints.

In no event do you have to look at the array of other trees' box summaries (via clicking to view Tree hints) and look at the entry in another tree, before clicking to "ignore," nor do you have to look at any tree hints in a search-results list (if you should do a search from this person in your tree).