You must first hack your PSP, then use the XMB switcher to switch USB mode to UMD, then connect the PSP to the PC. Poof, you get access to UMD contents. Make ISO from that (note that for MUA2, due to it having anti-piracy protection, you will have to resort to more complicated hackery programs), put it into ISO folder on the PSP (the "hack" part covers getting that). Apply mods as necessary.