This is going to be a tut on how to Make a Custom Comment with your jailbroken ps3. You do not, i repeat Do NOT need to have singed in with your jailbrake for this to work.
First you will need to create a new user that you will sign into when you data transfer.
You will need this file for this to work, or you can create your own.
This is a simply fairly TuT but if you dont follow instructions, you will mess it up.
1.First we will need to edit the mecomment.dat
2.Open it in a hex editor of your choosing.
3.Clear any thing thats in the mecomment.dat.
4.To go down as pictured in xSTiNkY_FinGeRsx's comment, you will want to put the hex code 0A in about 11-13 times depending on how far down you want your comment to be.
5.Now you can enter the text you want in. You could be like xSTiNkY_FinGeRsx and show off your challenge lobby skills or you can do your own thing. Just make sure that the comment is less than 50 charachters. Ive gone up to 63 before but i wouldn't push it.
Now save the mecomment.dat
First start your ps3 in JB mode.
1.You will need some sort of ftp server.
2.Now start up the ftp server of your choosing.
3.Go to the directory dev_hdd0
5.Then The LAST folder that has numbers (this is the new user you made at the beginning of this tut.
6.Then you will want to make a folder in the new user directory called friendim all one word).
7.In that folder, you will want to put your mecomment.dat in there.
Now exit out of the ftp server.
Now you can data transfer.
Once you have data transfered, you will want to sign into the psn with the new user acc you made on your jb. Then your custom comment will be there!