there shouldn't be any trouble with voltages up to 12v - probably not over that either, but it is possible...
things are triggered at much lower voltages - they are often just looking for a rising edge
an attenuverter would not do that - what you are describing is an offset, which may be part of an attenuverter module, but not the attenuversion (which is attenuation and inversion) - modules such as happy nerding 3 x MIA and mutable shades can do this , but a basic attenuverter may not! BUT this may not work if the module being triggered is looking for a rising edge at say 3v to open - you'd probably be better off amplifying the signal - this can often be achieved by multing the signal and then using a simple mixer to amplify the signal by 2- so from 0-5v you'd get 0-10v
if you don't have attenuators or attenuverters yet - then I'd advise getting some - mostly for controlling modulation - 0-10v (full range) on a lot of modulation inputs can sound crap - whereas 0-1v (a smaller range) can sound great
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities