Create a new calalog file on catalogs/nebulae called nebulae_LMC.sc where you copy the catalog data. Open config/universe.cfg and on the tag NebulaeCatalogs, add the following line : "catalogs/nebulae/nebulae_LMC.sc".
Don't forget to copy the catalogs in catalogs/nebulae/nebulae_MilkyWay.sc. There are also a catalog and a model for M16, with model grouping enabled (even if the feature seems to be not implemented), and more realistic orientation.
I decided to release this buggy M82 model, with two intersecting sprite which are flickering. I hope model grouping will be implemented soon to solve this problem. Don't forgot to paste the catalog file too, by replacing the old "M 82" instance, and adding the new "M 82 Starbursts".