Repeat Nitrocarburizing

I have a requirement to rework some machined parts, described below.

Base material: - Orvar to DIN 1.2344

Treatment: - Nitrocarburize to 1250 HV

Could you please tell me if there will be any degradation or loss of performance, to the base metal or surface treatment properties, if the Nitrocarburizing process is repeated a second or third time on a machined part?

Well, your total case depth is going to increase each time you reprocess. Depending on the configuration of the part, this could cause a brittle failure.

Well. Your application and product profile to be considered before doing a rework. You can minimise the case depth by heat treating it at a higher temperature and potential, with shorter times. That is the only way you can do a rework without destroying the basemetal.
However if the product is thinner, it may not work.