Scalpel or chainsaw? The subject of extending vanilla object behavior.

I'm currently working on a mod that will extend glass panes into staircase blocks. This mod involves tweaking some behavior of vanilla objects, and implementing a new render method for the hybrid block.

The way I see it, I have two routes to an end here.

The first approach is to use class transformation to surgically alter the methods of interest in the vanilla blocks. This is of course a coremod, which seems heavy-handed for such small behavioral changes.

On the other end of the spectrum, I can create new blocks and inherit what I can from the vanilla objects (private and final modifiers are giving me headaches, of course). I can then try to replace the vanilla blocks in the registry with my new copy.

I guess what I'm asking is, what's the preferred way of extending vanilla object behavior?