In non freesat mode on my Humax FoxSat HDR all Channel 4 regional variants look the same. All are 10714 H 22000-5/6.
Is there a way to see the SID or VPID on the Humax?

Looking at the LyngSat website Channel 4 Midlands is the third entry in on this transponder. Can you assume that the third entry on the Humax is the same channel?

Can't answer your other questions but,AFAIK, all the programmes will look/be the same on the regional variants but the content of the ad breaks may vary

And who cares about adverts anyway?! It's not like Ch4 carries regional news/programmes

You can't display the ID's to tell which is which but there are two Channel 4's and 4+1's on the epg.

104 Channel 4
121 Channel 4 + 1
974 Channel 4
975 Channel 4 + 1


Which is which variant, not a clue .

I believe that on the Freesat EPG on 104/121 you get the C4/C4+1 variant dependant on your Post Code (like BBC & ITV). I get C4 North. 974/975 are the London ones which have 'Audio Described' enabled (the others don't).
In non-Freesat mode I think you can safely assume that the channels listed are in the same order as shown by Lyngsat. I did a test and retuned them and London (with 'AD') came up first.
Like others have said, apart from the benefit of 'AD' only the ads are different.

It doesn't matter at present as its just adverts that vary but I hope that if Channel 4 do ever transmit regional variations they will include the region in the name as in BBC 1 West Midlands. There are 6 variants.
Channel 4 London SID 9211
Channel 4 South & East SID 9212
Channel 4 Midlands SID 9213
Channel 4 North SID 9214
Channel 4 Northern Ireland SID 9215
Channel 4 Scotland SID 9216
On my Dreambox I can see the stream info which includes the SID which is different for each variant.