I use the cartridges the opposite way around, CLI-8’s in place of BCI-6’s, and no conversion needed, but when buying OEM carts the CLI-8’s are cheaper than BCI-6’s, and you get a free chip...
I also sometimes use the cartridges the other way around and to use PGI-5 cartridges instead of BCI-3e cartridges a small modification is needed.
I also wonder if BCI-3e/6 cartridges can be modified to replace HP 364/564 and similar cartridges. You would then get very high quality transparent refillable cartridges for HP.
I think the modification would be possible by sacrificing the HP cartridges and glue pieces cut from the HP cartridges to the Canon cartridges. Here is an HP 364 and a Canon BCI-6 cartridges: