Private networks are different from local insertion, as I'm sure peds48 knows.
If your SWM system does not use coax networking (as most commercial systems do not) it is possible to diplex in programming on broadcast frequencies and then break it back out with a splitter at the other end. Then you would just use the TV's antenna input to get that programming.
The trick is getting that content on the broadcast frequencies. In the old days we would use a cheap RF modulator. Today, if you want HD programming, it's a little harder. QAM and ATSC modulators are very expensive and generally depend on encryption.
As I said, if all you want is SD, it's not hard. Use a diplexer like an NAS STD-9501M (I will leave it to others to provide a link, or Google can be of help) or if you are using SWM8s, you can use the off-air port. Then put band stop filters (again, I will leave it to others to provide a link) at the connection points to every receiver. Put a SWM splitter before each receiver and run one cable to the TV's off-air in.
If you are using canned programming, you may want to look into upgrading to a DRE system which lets you do insertion of canned programming right into the guide. It does not let you insert live programming.
There are other options but they get progressively more expensive. If you want to continue this conversation, I can probably help you more efficiently through private messaging and am happy to do so.