Would reflavoring things be ok?
For example, let's say i wanna make a wild west themed setting in Dragonbane, using the same rules, kin, spells, monsters etc from the core book. But sense it is wild west, i want characters to have firearms, but rather than making an "firearms" skill, i make a box that says "in this setting, characters uses the crossbow skill to represent their skills in firearms, and firearms uses the statictics of crossbow weapons."