I recently asked a question where I used the word "possessivize" because I didn't know the appropriate word. Is there one that's more appropriate?
Oh, certainly, possessivize is a perfectly cromulent word.
It's just not used very often because people don't discuss grammar seriously very often (I often claim that grammar is the last taboo subject in America — bring up a grammatical topic next time you're at a cocktail party and watch what happens).
But I assure you that any linguist could rip off a possessivize or two without batting an ear — when talking, for instance, about vowel changes in genitive case forms
It's just a technical term, is all.
It depends what you're looking for in a word.
If you're looking for the latter, I don't believe there is such a word. You have to use the phrase "to make possessive".
Alternatively, keep using the word "possessivise" or "possessivize" (as many people are already doing). Everyone will know what you mean. It will jar for them, as described above, the first dozen times or so they see it. Do it enough, and encourage enough people to do likewise, and it'll be a dictionary word within 10 years.
Remember, there was a time when blog wasn't a word.
Possessivize appears in Google results about 160 times, often used in the way John Lawler mentions. On the other hand, possessivate appears fewer than a dozen times, with most appearances stemming from one source (regparse.c).
Usage frequency aside, either possessivate or possessivize might serve as verbs meaning to make possessive. But as a word, possessivate possesses two advantages over possessivize: it is easier to pronounce, and it is more-obviously not a misspelling of possessive.
Use of the -ate suffix to form a verb seems as valid, or perhaps moreso, than use of the -ize suffix, -ate, like possessive, being of Latin origin, and -ize of Greek. (As a parallel example, we have motive, of Latin origin, forming motivate rather than motivize.)
Among relevant words in the small file linux.words, the -vate form predominates with 14 -vate verbs, seven -vize or -vise verbs, and at least one word (private) irrelevant: activate, advise, aggravate, captivate, cultivate, deactivate, devise, elevate, enervate, excavate, improvise, innovate, motivate, passivate, private, reactivate, renovate, revise, salivate, Slavize, supervise, televise.