Export xf_option, xf_option_group, xf_option_group_relation tables from board A
Export xf_option, xf_option_group, xf_option_group_relation tables from board B (as a back up)
Import xf_option, xf_option_group, xf_option_group_relation tables into board B
Run query on board B: DELETE FROM xf_data_registry WHERE data_key = 'options'
Log in to the Admin CP, check.
Should do it.
I have to put a disclaimer on this, though: I've never tested this. It could have undesirable results. Also, make sure if you're exporting options belonging to add-ons that you have installed the add-ons before importing all the values. If you don't, you'll see things like missing phrases everywhere.
It's also worth noting that there may be associated data not populated where it should be. e.g. Some add-ons/parts of the core may take a saved option value and do something else to some other data somewhere else. That's rather vague, but just bear it in mind if you find that some options don't work as expected. It may require you to go into the option, change the value, save, change the value back and save again to make sure everything works as designed.
What I'm basically saying is: Make a backup of everything before doing this, and be prepared to revert back to a backup if anything goes wrong.