reftex-format-label-function

reftex-format-label-function is a variable defined in `reftex-vars.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
Function which produces the string to insert as a label definition.
Normally should be nil, unless you want to do something fancy.
The function will be called with two arguments, the LABEL and the DEFAULT
FORMAT, which usually is `\label{%s}'. The function should return the
string to insert into the buffer.

You can customize this variable.