The 'mode' parameter and related code was effectively removed from ver 0.05 to 0.06, hence the lack of documentation. It appears that Acrobat 9 did not correctly render type 3 fonts. (See the Changes file in the current stable release.)
I am willing to see about the practicality of fixing the code so that this parameter is available if it can be done in a way which does not break current functionality. To that end, I have re-instituted the removed code in a patch pushed to the bugs/62108 branch in my github repo. A zip'd copy may be had here:
https://github.com/cnighswonger/PDF-Reuse-Barcode/archive/bugs/62108.zip
As I really do not have time to do a bunch of testing on this, I will rely upon others to do that and report back here how things stand. Hopefully this will become stable enough to be merged back in as part of a future stable release.