Please read the Universal Special Rules section of the BGB. If a character joins a unit with Infiltrate and he does not have it then the squad looses it and are not allowed to infiltrate. Same applies to things like (but not limited to); fearless, scout, move through cover, fleet, and hit and run. And in MOST cases the reverse is true.. a character with any of those special abilities joins a squad who doesnt have it then he looses it as long as hes with the squad. There are always special situtations when the above is not true though and it is always best to read the rules in question.