How do I convert bbcodes?

[Zaiaku]

I did a few searches but haven't been able to find an answer so not sure if I used the right terms, some mods have this options but doesn't would work with generic customer bbcodes.

I need to be able to convert some of my own customer bbcodes to newer ones.

converting some:

[tag=option]Something always goes here.[/tag]

to

[newtag]Something always goes here.[/newtag]