This is a fun hack I've found many years back. It should work with every RGSS version so disregard that we're in the RGSS3 subforum. The used graphics library not only implements the 3 blend types (normal, add, sub) we all know and love but also 4 additional ones: multiply, screen, lighten, darken. Descriptions with examples can be found hereand on many other websites. Maybe somebody out there has a use case for them. Feel free to use the script in commercial projects or adapt the underlying concept to font sizes without having to credit me (I'd still appreciate it though).
This script (written by me) circumvents the bad value check by temporarily pretending to be a “good” value. This is possible because the argument to #blend_type= is unnecessarily converted to a long (or int) two times: for the check and for the internal blend type assignment; and because the conversion function sends to_int to “unknown” objects.