Bit of a late answer, but it's been a while since I logged on - moving back into aerospace so, I'll be on more often I think
In answer to the question, yes it's possible to make minor mods to the interior of a specific MSN.
Typically 3-D printing is used to make prototype parts which will be used to verify fit form function, prior to going to the expense of tooling up.
If you were looking at going directly to the use of a 3-D printed part as part of a mod, then bear in mind that the materials will need to be compliant with the fire regulations of CS25 (853 if my memory serves). The material will also need to be certified and from a reputable (repeatable) source.
Your DOA should be able to tell you if they can do this in the application you are thinking about - talk to your CVE, or HOA.
I hope that this helps.