I know that you can change @grid-float-breakpoint in the \"variables.less\" file which compiles into the bootstrap package we all download and use (I think).
If you are using the SASS version, you'll find that variable in bootstrap/_variables.scss around line 286 and onward.
The further you go down that file, the more math and options you'll see.
I post that because people might come here looking for the SASS answer.
It really is better to recompile your file, but if you are making exceptions to rules, it might be better to make a new ID or CLASS to refer to whatever you are doing.