Standard - the opening is the standard size, either from the OEM or based on the measurements of the exposed area, to fully mask the negative
Bordered - the opening is a little larger than standard to expose part of the rebate of the negative. This is mostly for printing a black border around your image. Note this can impact flaring.
Full-Frame - the opening goes all the way to the film edge exposing the entire rebate (including frame numbers and, for 35mm, sprockets). Due to potential flatness and flaring issues, this is best used when you want to specifically print the entire rebate.
No, they are not adjustable. Fixed size only, but available for different formats. The 35mm holder shows about half of sprocket holes on the longest sides.