I recently made changes to template and node.tpl files for my theme. Is there a recommended way of implementing preprocess changes as to not hard code them into these files (in case of theme updates) or am I going to have to re-code them after theme udpates?
In an ideal world, you would create a sub-theme off of your master theme. For example, most people don't use the Omega or Zen themes directly; rather they use the starter kit which is included as the basis for the sub-theme.
The sub-theme will inherit features from the base theme, but allow you to customize as needed. When the base theme gets updated, the sub-theme doesn't get touched.
Whether you can retrofit your theme to actually be a sub-theme depends on your situation, but I suspect it is possible.