No actually, a certain ritual has to be done, which is also how they replaced Rin's "mana link" (
) from Ero method into little crest (dolphin!) one.
If I remember correctly, Shirou once complained in the game that Kiritsugu didn't even bother giving him the Emiya magic crest.
That being said, it is extremely unlikely someone would give their magic crest to anyone not blood related to them, due to the origin and purpose of the crest.