The thing is I didnt like the MyBB table layout for postbit_classic, and completely rewrote it in css keeping only the variables there. My qn is should I be careful of installing plugins because of this? Are they dependent on the table layout elements, or are they plugged into the variables?
Yes some plugins will look for default template structure in the postbit template, if you use a custom template there is a chance that some plugins wont work properly.
Ah..So overall it would be best to revert templates to default, install it, then do a diff on the template for changes, then add it to my theme myself..
No need to revert. Look in to the default templates and see which templates are newly added. In your theme it will be probably misplaced. Just move them to correct location.
No need. While making template variable edit in plugin, you specify sid, where if you keep sid=-1, it'd make changes in all templates.
But yes, if you use some variable in those template as a reference and in a custom theme, that variable if isn't present or far away from desired place, then it'd cause a bit trouble. But you could always copy that variable then and move it to the place you like.
So hooks are only around variables, and not html elements like <td>$somevar together?