There is a default key in Lotro for assist that bound to "F" by default. No need to waste a slot.

I've had better luck splitting my select/assist into two keys, or using a PressAndRelease style key. One of the things in Lotro that needs a fraction of a second to do is changing targets. Doing two target changes (F2 followed by "F" for assist) needs just a hair more time. Setting up a key to send F2 on press, and F on release seems to work well for me.


Also bear in mind that if you ever do a skirmish or your leader has a pet, F2 will get tripped up on you minion. F2 once selects the character, then any further presses cycles through pets/soldiers. The easiest way to get around that is to send F1, then F2. F1 selects yourself first, forcing the F2 to select the character, and not the pet.