Just to clarify, you're asking us to go the HTML4 approach of hard coding tags versus the HTML5 approach of utilizing CSS for styling?
If so, this is not a change we will be adapting, as it'd be a leap backwards in our standards compliant project. The reason it is set this way is so that interpreters can make use of the CSS and actually do changes on the fly as needed.
You're more than welcome to modify your licensed copy of UBB.threads in any way you desire (short of removing any html credits without proper licensing), but any modifications to the base product are unsupported.