Approved locations for decorations in the engine room are:
Walkways, provided they don't interfere with getting around.
Doorways, again, as long as it doesn't interfere with the crew moving around.
Locations that are strictly off-limits:
My office.
Anything vital to the running of the ship.
Anywhere you think might interfere with running the ship.
And yes, you may wear your costume provided it doesn't have any bits sticking out, or anything hanging off it, or anything that might catch on something, get caught in something, or otherwise impede you in your duties.
Walkways, provided they don't interfere with getting around.
Doorways, again, as long as it doesn't interfere with the crew moving around.
Locations that are strictly off-limits:
My office.
Anything vital to the running of the ship.
Anywhere you think might interfere with running the ship.
And yes, you may wear your costume provided it doesn't have any bits sticking out, or anything hanging off it, or anything that might catch on something, get caught in something, or otherwise impede you in your duties.