This parameter used to be a string keyword accepting "yes" and "no" and was changed to a CCTK_INT in the ML rewrite. Making it a CCTK_BOOLEAN won't change it's C type (both CCTK_INT and CCTK_BOOLEAN are ints in C++) but will let users use the same parfile with both pre and post-rewrite code (or alternative the same code with pre and post-rewrite parfiles).
If we really cared about the speed we may consider making it a CCTK_REAL so that
ifthen(v==1, a,b) could be written as
ifthen(v, a,b) thus saving on the comparison operation required and on a int->real conversion.
This would require adding support for Boolean Parameters to Kranc's Param.m which does not seem difficult.