Here's the situation.
Up until firmware 3.10 we could use any ol' topmenu_plugin.rco file to edit our icons, but after the release of 3.10 we realized that our old icons were actually BRICKING our psps (never mine, of course

). Anywho, in order to use older topmenu_plugin.rco files, you must first use the converter to allow them to work on your 3.10 + psp. Word is you have a 3.40 - so here's what I'd do.
1. sign up with the site
2. download the file
3. convert your topmenu_plugin.rco file of your choosing
4. flash it to the psp and enjoy
It may end up that you never needed to use the converter, but it's always better to be safe than sorry.
-DarkPacMan77-