That depends on what you mean by "make a match with a person already in Geni". If you mean you have merged a Profile you manage with one Managed by someone else (and it is an unclaimed Profile) - then it is possible for you to add information, change information, etc without anyone's permission.
Should you? That depends. If it is a close relative of the other manager, and they are active, I think it might be more polite to first touch base with them.
It may also depend on the information - for example, a list of arrests and convictions vs A note about where obit can be found.
Under what circumstances you add info without saying boo to anyone vs when you check in, make sure others okay with it --- I suspect lots of different standards there.
