I'm not sure when I discovered this, or if I've ever seen this posted anywhere, but this is a simple trick with multi-line comments I use when debugging code:
//*
Uncommented code
/*/
Commented code
//*/
To change this around, just remove the first /:
/*
Commented code
/*/
Uncommented code
//*/
What is going on is /*/ will always toggle commented to uncommented and vice versa. //*/ always ends a multi-line comment without causing a syntax error if there wasn't a multi-line comment before it.