Thanks for your response. I'll list the steps I followed below.
1) installed Bruteforce 4.7.4 and and PS3 Tools.
2) installed GT5 on my console again, started career mode to create a save and then put it on my USB and onto my laptops desktop.
3) Opened Bruteforcd, updated cheat repository and clicked close when it asked me to set up a profile.
4) Set up a template PARAM.SFO using the save I took off my console so that my profile name and number then appeared at the top.
5) Edited global settings and input my user ID and console ID which I obtained from opening my Param.SFO with the Param editor.
6) Unzipped the saves I downloaded that I wanted to resign and refreshed directory so they appeared on screen.
7) Selected the save I wanted to resign and clicked full rebuild at which point it asks if I want to rebuild using my profile and then warning as the save file may not be decrypted and I click yes to both.
Nothing happens and the profile ID on the save doesn't change to match my profile ID.
I've tried various other things such as update account ID and copy Param but that doesn't seem to work either.