Being able to customise an o-ring design to have the exact ring you need is great and very convenient. But the actual design you end up with still has to follow some rules. You can still technically create any combination of features you want, of course, but for usable o-rings, you'll have to pay attention to some restrictions.
The Purpose and Material of the O-Ring Determine Much of the Design
Some features of o-rings are very specific. Colours, for example, denote materials and either purpose or condition, such as something used in low temperatures or something used in solar-panel installations. So, what you plan to use the o-rings for really determines much of their design already. You wouldn't use a quad-ring design when you really need a flat o-ring design for example. There can be some flexibility, of course, and no pun intended. you can speak with the company that will produce the o-rings to find out their recommendations.
Mixing and Matching as Needed Is Possible
You can mix and match features as needed, although you'll be limited by whether or not the combination can be actually used. A use for green o-rings (which are used in high temperatures) might not match with a use for a quad ring design (which is used in low temperatures), so you wouldn't make something like that except for use in a class where you were showing students how not to design an o-ring.
Size and Thickness Are the Most Customisable
The features over which you have the greatest control are the size and the thickness of the o-rings. Any o-ring of any colour or material with any groove/edge shape can be any size or thickness, limited only by what the manufacturer's machines can produce. You don't have to worry that you won't be able to get a red o-ring in the size you need, for example, or that you can't get a blue quad ring that's X centimetres in diameter and Y millimetres in thickness. As long as the manufacturer's machines can produce something in the size and thickness you need, and as long as they can obtain the material you need, you should be able to get the o-rings you need.
Meet with o-ring and gasket manufacturers to find out their factory's limits and what they'll need from you to produce the design. Be sure to ask if they have a designer on staff who can help you create any files needed so they can produce the exact items you need.