Call CMA (Citizen Machinery America) and talk to them. This switchover isn't as simple as one M20/M21 command as it would be on a machining center. There are a great many offsets, macros and sub-programs that come into play here, and all of those must also be converted over to inch format.
For instance. moving the tool slide that carries your T1 through T6 turn/groove/thread/cutoff tools up for indexing send the slide up. Lets assume the distance from the X0 point to the uppermost position is a diametral 60mm in X and the distance between two tools in Y axis is a linear 30mm. The sub-program call for lifting the tool in X and moving over in Y will be written as X60.0 V30.0, so you'd need to change it to X2.3622 V1.1811.
You'd need to get advice (and perhaps programs and parameters) from CMA to make the change.