If you want to either plan or reduce observations made in your own non-standard system, both the planning and the reduction programs let you declare the system as NONE or OTHER. Use NONE when you want to work entirely in the instrumental system, and OTHER when you want to use a special system of standard stars. In either case, you will need to specify central wavelengths, bandwidths, and the relation between the passband magnitudes and whatever color indices you use.
You can maintain your own files of standard stars for your private system, or for your instrumental system. Sometimes it is convenient to maintain instrumental-system standards, to avoid the information loss of conformity errors, which should be negligible in this case. Instrumental mean values can then be used to determine extinction very accurately.