On my previous car I had a urethane front bumper which I cut in order to fit a big FMIC, but urethane isn't that easy to cut. It didn't turn out good at all. Others have probably had better experiences trying to cut polyurethane but I wouldn't do it again unless I had to.

 

set of tin snips works best. then use a flat board with really aggressive sand paper to sand smooth the cut marks. you can make it look 100% pro if you take a little time. i went a step farther and cut out the whole dam area. but i plan to get a new aftermarket bumper anyways so i didn't care to much. would be plenty of support either way you do it. remember all the plastic underneath the car all bolted together.

 

ok bad pic, hard to see it. post another later