Yes, it is possible, i have found these guides:

1. From 1.50 to 3.52 M33

2. To 3.52 M33-4

3. From 3.52m33-4 to 4.01 M33-2 and kernel 1.50 (english)

I'm moving from 1.5 to 3.52 M33 at the moment, i'll let you know how it happened ^_-
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I think that after you have installed at least 3.52 M33-4, you can upgrade to any version you want. I suggest to take the latest one, which is the one you mentioned, 4.01 M33-2.

Don't forget also to install the 1.50 kernel addon for your custom firmware, as you'll need it for running almost all homebrew software.
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I've followed the 3 guides and now i'm running firmware 4.01 m33-2 and kernel 1.50. I've tried snes9cTYL and it works perfectly
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Excellent, it just shows that what looks and sounds like a scary process, is in fact, quite an easy process - as long as you follow the instructions (and get the software required from a reliable source...)

Opens up a whole new world of gaming...

Now if only I could get Pokemon Snap working on it properly...
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glad you got it working.
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Yep, glad you worked it out. Now you can enjoy loads of great emulators, homebrew and games.
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Amazing to play super mario world on a sony psp... My daily train trips are gonna seem shorter and shorter
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