Hello! Elgg is open source, can I modify it as you wish?

I know that if I change, my network future may not be updated, if not be able to use in 1.12.12 then make it 2.2 or something.

What I want is to modify the entire nucleus, And in each update always pieden plugins, and there are things that make me difficult to variables, good link so to speak, then I want to change it,

For the plugins I'm using leave everything as equal, only modifies the variables.
example:

elgg_register_event_handler ('init', 'system', 'google_init');

I change it to a name:

socialnetwork_register_event_handler ('init', 'system', 'google_init');

the name elgg change to socialnetwork.

Is it possible to make those changes?

elgg the license says I can:
modify the kernel, but if I distribute the modified version is illegal, but if I use it for their own use is legal and whether it can be done.