Problem is we're number 1 or 2 for most of our search terms and I'm #*$! scared we'll lose them.

The current structure is like site/folder/page-name.html and the new url would be site/t-5/page-name-page1.html

I'd of course do a 301, first of all, would altering the structure hurt my rankings and second is the suggested structure recommended?

I'm torn, as I need to alter it, to expand the site but I'm concerned I'm going to screw up years of hard work.