Bigbad
No you can not add opening doors to planes that do not have them this is done at the time of creation.
Also some planes use the wingfold and tailhook opiton to open cargo doors and let down stairs with. A good designer will include a readme that will let you know how to operate the various doors and stairs.
A good example is the IFDG B767-300ER it uses the wingfold for the cargo doors and shift e for the main door.
