I am looking for a cheap, preferably free, program or suggested work flow to make changes or additions to a STL. The particular interest right now is a small mouse that I download from Thingiverse that I'd like to add a block letter to. Something I'm trying to do for an event at my dog club. I want to print it in green with a block "Q" on its rump. I have windows 7 and 8.1 along with Linux Mint and will soon have an Afinia printer.
Thanks in advance for any pointers,