Removing the apical meristem (growing tip) of any branch or stem permanently terminates it's growth. There is a growth regulator produced in the apical meristem that suppresses lateral growth along that branch or stem, so when it's removed, another growth regulator becomes dominant and stimulates new lateral growth - usually from leaf axils (crotches) along the stem/branch.

Right now isn't exactly when you'd expect the most robust growth on your avocado, so be patient - it will happen as days lengthen & the plant wakes up.

I can't advise you about whether or not it's safe to fertilize w/o knowing something about how you water. We can talk about that, and I can help you with an easy way to make certain it's safe to fertilize if you wish. Plants cannot grow normally unless all the essential nutrients are available for uptake. When plants are growing in container culture, you shouldn't rely on the soil to provide them, because it can't/won't, so it's very important that you provide them via fertilizer. The question now is, can we safely add fertilizer to the current level of salts in the soil or should we flush those salts from the soil first?

Al