Lyon train stations

Just stick to your plan. You will be protected if the first train is delayed. 12 minutes is plenty of time.

If you are worried about the time to change, spend a tiny bit more money and get the tram from Perrache to Part-Dieu, leaving a bit earlier.

You do not say the date and departure time, and if you are going to Aix-en-Provence or Aix-en-Provence TGV. If the 1st train is a TER, you can just take an earlier train. If it is a TGV, it originates at Lyon Perrache and should leave on-time and is is only 9 minutes to Lyon Part Dieu, so unlikely to be delayed.

It's the TGV station in Aix.

When you say "originated" does that mean we DON'T change trains in Part-Dieu? The first ticket has no assigned seats and the 2nd one has reserved seating.

Originate means that the train starts there, Lyon Perrache. It is not coming from somewhere else where it can get delayed. You have not told us the time or date, since you say it does NOT have seat reservations, I can assume it is a TER. Let me guess, 11:20 am? If you are worried, you can take the TER at 11:01 am. That does not originate at Perrache, but at another Lyon station, so should be fine. TER trains you can take anyone that day on that route. So if you took that one, you will have about 30 minutes at Lyon Part Dieu. Time enough to get bored.

Ha ha - how did you know it was 11:20? Are you reading my computer? :)

Just hoping train #2 is right across the aisle from train #1 so we don't have to wander around in a strange station looking for a certain track.

Not too hard to figure out. The 11:20 is the only TER with a 12 minute connection time at Part Dieu to a TGV direct to Aix-en-Provence TGV.

It is unlikely that the tracks will be adjacent. The French are not as forthcoming about the platform assignments as the Germans and the Swiss. You may not want to bother sitting down when you board at Perrache, as the next stop 8 minutes away is Part Dieu. Just stay in the train vestibule with your luggage and exit immediately when you arrive. Go down a level to the corridor and stairways and escalators take you up to your new platform. The Man in Seat 61 says it should take you no more than 3 minutes to get between any two platforms. The Tracks at Part Dieu have letters, not numbers (the French have to be different) There are 5 island platforms with a track on each side and a platform with a single track, ganged like this: A-B, C-D, E-F, G-H, I-J, and K. Here is a picture of the connection corridor.
https://www.google.com/maps/place/Lyon+Part+Dieu/@45.7604772,4.8594722,2a,75y,104.63h,88.15t/data=!3m7!1e1!3m5!1sdjVESfm05S-fsS65PlPCqQ!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D1.8532062134799787%26panoid%3DdjVESfm05S-fsS65PlPCqQ%26yaw%3D104.62925468080392!7i13312!8i6656!4m6!3m5!1s0x47f4ea62fdaf6429:0x6e097152ab2851f8!8m2!3d45.7605474!4d4.8611177!16s%2Fm%2F025zsp_?entry=ttu&g_ep=EgoyMDI1MDkxNy4wIKXMDSoASAFQAw%3D%3D

If the train originates at that location it will be in place at least 10 minutes prior to the boarding time (usually).

If your ticket doesn't have a seat assigned you probably bought it from a second vendor, not the rail line. All French trains (from my experience) assign seats. You may want to go on the lines website a day or two ahead of the departure and see if you can get a seat. Not having one can be a hassle as someone may have the seats you plop down in. And they will want to sit there.

The main train station in Lyon is very big, and confusing. The smaller ones are pretty easy to navigate.

TERs from Gare Perrache do not have assigned seats. The OP is taking this to Gare Part Dieu to get a TGV for which they DO have assigned seats,

The main train station in Lyon is very big, and confusing

But it really is not confusing. It is a corridor running beneath a series of boarding platforms, well marked, with a stairway, and perhaps an escalator to access each of them.

Yes it’s crazy. It’s not 12 minutes, it’s 10 if the first train is on time because train doors shut 2 minutes before departure time. Part Dieu’s trains all dump into the crowded main station area, not one of those neat and easy underground corridors. Yes, you can throw away your TER ticket. This isn’t like an airplane itinerary. Your TGV won’t be invalidated. In fact those are separate companies issuing the tickets separately.

An easy option, just take an earlier train between the two stations. Your ticket is valid for any TER on that date.

Finally found a way to see the train schedule on the SNCF website (pretend you are buying another ticket). I see there is an 11:01. But I may just opt for a taxi if there is no cancellation penalty. Thanks for the info.

I’d be at the station minimum 20 minutes before, if not 30.