Renumber Second Branch

Whats the syntax for renumbering the second branch only??

example, its currently {1;2} would be {1;0}
and
{5;2}
{5;3}

gets turned into
{5;0}
{5;1}


Renumber Second Branch.gh (13.1 KB)
thanks in advance.

Renumber Second Branch_re.gh (14.6 KB)

thanks!! thats pretty much what i ended up doing – when i posted i was having a bit of brain fog.

Would still like to see a path mapper solution if it’s possible.