Not entirely sure I understand what you're asking.
- This program is going to be broadcast on your local PBS station, and you want to re-run it on your local-access channel?
- This program is going to be available from PBS, but your local PBS station isn't going to broadcast it, but you want to run it on your access channel?
- Your school district sends any local programs you want to air to the PBS station, and they put them up on the local-access channel?
- You have some equipment at one of the school buildings, which plays programs that air on the local-access channel when it isn't running PBS programs?
I suppose the local-access channel is probably standard-definition; American Experience is HD.
If the program is going to be broadcast, I think I would arrange to record it on a DVD recorder. That process would automatically downconvert it to standard definition. And, most facilities that can play back TV programs can use a DVD as a program source. (either directly, or by dubbing it into a hard-disk playback system) You'd probably want to ask several people to record it, as at least one is probably going to make a mistake
If it's *not* going to be broadcast, then it seems to me the PBS station is going to have to record it for you, and how they handle that depends on what kind of equipment they have available. I would think they should be able to make a DVD for you. For that matter, if they're responsible for programming the community-access channel when you aren't, then I would think they already have the downconversion equipment (and the playback equipment) and they should be able to handle the entire process.