For an example, say copying the Arcean battleship template to the Terran style, you'd need to:
1) Rename/copy the appropriate .shipcfg so that it is classified as Terran. So you'd find S3_Battleship.shpcfg, and change it to something like S0_Battleship_3.shipcfg.
2) Copy the template xml to a new file. From BattleshipTemplate_t.xml to BattleshipTemplate_3_t.xml in this case.
3) Edit the new xml to use the copied shipcfg. Just change the <Model> value to the shipcfg's filename without the Sn_ prefix, so Battleship_3 in this case.