Well, it can be bitset, kind of.
The library codes are burned right onto -R media. With +R media, they are burned when the entire disc is burned. Bitsetting the codes on +R media, therefore, means that there is a single code which reads as DVD-ROM.
With -R media, you can burn a second code, and some players will accept it as the valid code. Some won't, though. Apparently this can increase compatibility, but nowhere nearly as much as with +R media.