If you mean change the image mode, then I've already done that...

or is 256 colours still too much?

88x88, the same as the default ones.

I recently got the Stage Roster Expansion stages working, so I was adding custom icons and previews for the new stages. After adding all the previews in though, the game now crashes at the stage select screen. Does this have to do with the file being too big? If so, how can I make it smaller?

Well today I tried getting some custom stages working, so I followed This Guide. I got the stages working with their custom icons and all, but I only have 30 custom stages, 7 under the max that the SSS has. So, I tried removing the lines with the extra stages I didn't need, but all that did was just change their icons. How do I completely remove them?

This is the code:

Code:

Maxed Out SSS [Eternal Yoshi]
046B8F5C 7C802378
046B8F64 7C6300AE
040AF618 5460083C
040AF68C 38840002
040AF6AC 5463083C
040AF6C0 88030001
040AF6E8 3860FFFF
040AF59C 3860000C
060B91C8 00000018
BFA10014 7CDF3378
7CBE2B78 7C7D1B78
2D05FFFF 418A0014
006B929C 00000027
066B99D8 00000027
00010203 04050908
0A0B0C0D 0E0F1114
151A1917 06131D1B
1C1F2021 22252423
27280710 12161800
006B92A4 00000027
066B9A58 00000027
1E262A2B 2C2D2E2F
30313233 34353637
38393A3B 3C3D3E3F
40414243 44454647
48494A4B 4C4D4E00
06407AAC 00000090
01010202 03030404
05050606 07070808
0909330A 0B0B0C0C
0D0D0E0E 130F1410
15111612 17131814
19151C16 1D171E18
1F19201A 211B221C
231D241E 251F2932
2A332B34 2C352D36
2F373038 3139323A
2E3BFFFF 40204121
42224323 44244525
46264727 48284929
4A2A4B2B 4C2C4D2D
4E2E4F2F 50305131
523D533E 543F5540
56415742 58435944
5A455B46 5C475D48