Not sure what the problem is. Are you changing the right part for the spawning of blocks. Also don't forget that there are only 6 types of normal block plus the special, the other blocks are for "different states" for example for dragging block 1 it shows frame 2.
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That seems to work when I test it. You might have to play around with the numbers to get the right frequency of special blocks to normal.
Another feature of the original events is that it removes matches when spawning the new blocks, which may give the impression that the frequency of blocks is unchanging. If you want to play with that it is event 39 in the event sheet.
As for the special block I think it does nothing because angeltekno hadn't got spawning working as planned yet. I'm also guessing that the special block may have been a wild card for example if you match 2 purple then a special it would count as 3 purple. But like I said I'm not sure what the original idea was for the special block.