Saddle rails are standard in size?

I ask as I wonder if I can just exchange the saddle without having to pay a visit to the bike fitter.

Also, from going from Ti to carbon, any changes need to be made?
Seems carbon rails are oval.

Thank you in advance for the help

Oval carbon rails may need a different seat post/clamps. If it is clamped top and bottom it should be ok but if it grabs the side of the rails it will need changing. With some seat posts (eg, Trek) you can change just the clamp to one suited for oval, rather than needing a whole new seat post.

Thanks! How about Braided rails?

Same thing.

Also not all rails are the same distance from the top of the saddle. And not all saddles compress the same under your weight. And the middle of the rails on one saddle bears no relation to the middle of the rails on another. Also the sweet spot for your sitz bones is in a different place on every saddle. Just putting on the new saddle with the rails st about the same place in the clamp is as good a starting point as any. But it takes some fine tuning to replace a saddle with another one of different make and/or model. I hardly think a professional fitting would be required to accomplish it. Sooner or later you should be able to know by feel and reference to your prior best fit how a saddle is placed wrong and when it is right.

Keep in mind as well that all saddles "break in" over time whether for better or worse. It is quite common for a a rider to sit lower in an old saddle than in the same model new one. At the very least the padding will compress permanently. So knowing how to recover your preferred riding position as a saddle ages is a necessary skill unless you don't mind paying for the same thing over and over again

Yep. Exactly right.

I use a level program on my smartphone to measure the tilt of the saddle as I adjust it. I put the bike in the same place so the ground is the same pitch each time, measure the tilt, and then test it. I find that even slight changes in the tilt are noticeable.

Fore and aft is pretty straightforward, most saddle rails have calibration marks. Same thing goes for vertical height (mark your seat post if it doesn't have marks). Tilt is the hard one to figure out and it can take a long time to get it right if you don't have any way to measure tilt accurately.

It's not hard to measure your fit position on the bike before you start adjusting. Write that down and save it. There are only three points where you contact the bike (pedals, seat, bars) so it's not that hard to get it right. I can generally set up a bike in about 10 minutes from out of the box and have it pretty close to where I like it.

Besides that, I've never had a bike where the seat post didn't slip some over time anyhow - so get used to learning how to adjust it.

J.