Thanks for the update .
We have done the similar activity on our test RAC before doing in production.
We have convert to native multipathing from RDAC , device name had changed and oracleasm identified this names. But failed to identify the voting disks and crs didn't start.
What we have done is we configure ORACLEASM_SCANORDER and ORACLEASM_SCANEXCLUDE.
Once this is configured it was successful.
You can find details here