variations come in 3 catergories, 1 for 1, which is basically a swap and is free, an application for more or different calibers which costs £26 last time i did one, and a change in conditions.
the first two require you to fill in the FAC application form, you don't need to add photos or details of your counter signatories tho, leave that bit blank. REMEMBER to add all the calibres you have inc moderators, ammo limits and type (expanding).
the change in conditions only requires that you send in your licence with a covering letter and any qualifications such as DSC etc giving reasons for cha