Alien3 hasn’t been here since 2010. His models were problematic in the technical sense. Their mesh shapes were OK but often unnecessarily high-poly with no LOD and his texturing was extremely inefficient and rudimentary. Lots of uniform colors from separate and needlessly large images.
Modification of his models might be possible, but would require his written permission, otherwise it would be an infringement of copyright. Have a look at the License tag in the config.txt files of his assets and see if they grant permission to modify.
