I think reference to online manual is ok, but what if a user doesn't have internet connection atm? Maybe it'd be good to go GIMP way and give the users an option to download the docs (in preferred language, if possible) to their HDD and have a link from the tooltips to this documents? It works fine with GIMP, so maybe here it will be good as well?

Not sure if possible / convenient, but what would You say for a specifically designed pop-up window (or whatever panel) that appears only if multiple objects are selected and some keyboard shortcut pressed? It could look similar (in some ways...) as outliner, containing list of values common to all selected objects (so a dynamic list). Then it can have a field near every value, in which You can put expressions like "+0,5", "*7" etc, and "0" (disabled) or "1" (enabled) where applicable. Near this field there could be a dropdown menu with the type of action, where You can choose "linear" or "incremental".