This service is intended to breathe new life into old optics. If you already have a telescope it doesn’t make sense to buy an entire new telescope if you only need a small change to specification. Most of the work has already been done after all.
Examples of revision can be as simple as refiguring lower grade mirrors to a much higher surface quality, turning a mass produced telescope into one of excellent optical quality. Such processing can be surprisingly economical due to the fact that we are not starting with a completely new mirror blank. Any type of telescope can be revised.
It is possible to go one step further and make more fundamental changes to the optical system. Such as changing the focal ratio, the back focus, etc. It’s relatively simple to make the telescope faster and have a wider field of view, the adjustment is made to the mirror and the telescope tube must be shortened. It’s also possible to make the telescope have a longer focal ratio although this almost certainly means a totally new tube must be made, which is still far more economical that buying an entire new telescope.
Each case must be reviewed individually due to the amount of constraints. For example a large change to the primary mirror of a newtonian telescope will almost certainly mean that a larger or smaller secondary mirror will be needed.