On April 3 I am flying YVR-YEG but connecting via YYC as no T+ was not available when ticket purchased. However I am quite willing to burn some credits.

AC 226 YVR-YYC is currently J4 R3 Y2, while AC248 YVR-YEG is J4 R4 Y0.

So I am thinking of upgrading 226, and see if I can get on 248 while at the gate despite there being no Y - they both leave at roughly the same time but by losing the YYC connection I get home 2 hours earlier and miss another flight on a Dash 8, far too many this year. Normally there would be a change fee and a Y seat, plus fare difference, but since I end up in the same place, there are currently empty sets, is it orth a shot?

Has any done something like this? Am I out to lunch or even trying? Will the gate agent laugh? Should I bring chocolate?

Definitely worth a shot - I've been told that there must be a Y seat, and also been able to make a similar change even if Y=0
FYI, there should be no fare difference for same day changes, just the change fee.

Confused... so you have a Tango fare ticket? And you are trying to pay the change fee, the fare difference and play the R game?

What I read into this is that the OP could not find Tango+ on the direct flight so he bought a flight with a connection, presumably in Tango+.

Exactly! All three non-stop flights that night had 0 tango + nor latitude, so booked connection since I can't book Exec on short flights. It gives me an extra segment but I would rather be home at 11 pm instead of 1:30 am.

Upgrade on booked flight has cleared so will give it a shot at gate. No checked luggage so that should help too.