You would need to expand the notes to fit the new BPM
i.e.
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changing the LPB from 4 to 8, using: ZL08 … (ZL04 after if you want to switch back) – The master track might be a good place for this command
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Double the number of lines in the pattern from 64 to 128
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Go to renoise Advanced Edit panel and use the Expand function on everything in that pattern
note: You want to choose the option Whole Pattern here, or Select everything in the pattern before hitting Expand.
dBlue also wrote a tool to help with more difficult LPB jumps which is worth a look:
https://forum.renoise.com/t/new-tool-2-8-3-0-flexible-pattern-resizer/30664