It's definitely doable since a few companies made the remote can ballasts to run either of those light sources but I wonder if there were any current or historical installations out in the wild that had HPS or MH clamshells. Especially any roadway installations. I know a few places converted their mercury clamshells to LED but that conversion is less involved than convert to a different HID source.

In my area, during the MV clamshell to HPS conversion, new arms were installed with HPS cobraheads.

Anyway any one here know of such installations, either still intact or historical. 

I do remember someone having photos of some clams that had the 360w Unalux lamps in them .

That would be interesting too and quite a boost in light levels compared to the original 400w MV.

On Washington Boulevard in Whittier, California, I have noticed some Westinghouse OV35 lanterns that have been converted to high pressure sodium that are used in a strip mall parking lot. They are still in use as of 2022.

Here is the link for them:

https://www.google.com/maps/@33.9721387,-118.0726259,3a,17y,168.67h,103.11t/data=!3m7!1e1!3m5!1soMTCLXAJcBCTPB_EvUV6cA!2e0!5s20210301T000000!7i16384!8i8192

In addition, I have also seen some GE Form 109 lanterns and Line Materials Ovalite lanterns that have been converted to metal halide, but were converted to LED instead of scrapped. These lanterns are located in another strip mall parking lot and are still in use as of 2022:

https://www.google.com/maps/@33.9487752,-118.0060927,3a,43.4y,1.47h,105.42t/data=!3m7!1e1!3m5!1sC3kTN0AEzH8czpNII5_4JQ!2e0!5s20211001T000000!7i16384!8i8192

Interesting, so far it seems like this practice is more or less been limited to privately owned installations. I suppose pretty much all public utilities opted to replace the luminaire instead.

  If there on 6.6 amps things are much harder but there 6.6 A HPS ballast out there with ignitors that if will start pulsing when It at OCV
 
  I do see remote ballast MH paint can MH now and then.