English Translation
I cut the pizza before I eat it.
What’s the difference in meaning between “comerla” and “comérmela”?
To be frank, they are quite similiar. IMO, Comer is more the activity, and comerse is more about a eating a specifc item (maybe like eat and eat up, in englosh). So, I’d say that the difference resides on whether the object in the sentence is whole or not. With that I mean:
if you are talking about what you do when you have a pizza in front of you (ie, you cut it in 8 slices) → comermela
if you are talking about what you do with pizza in general, a whole pizza, but also a slice, or just some pizza (ie, I cut my pizza with a knife before eating it) → comerla
That is not to say that comersela is not about a generality, what I mean is that it’s about the whole unit of pizza, and not just some undetermined quantity
And, as a disclaimer, this is just my opinion about it