Can I swap from 46/36 chainrings to 36/28? I ride a 2015 Cannondale CAADX (Sram Rival) which has an FSA Gossamer crankset fitted with 46/36 chainrings.  It has 5 bolts and a 110mm BCD.  I'm an old man with bad knees.  I never ride on the 46 ring, but I could surely use a granny gear.  Is it possible to swap my chainrings for a 36/28 pair, e.g., say a Vuelta SE Plus Chainrings 110mm BCD Black 36T and a Vuelta SE Plus Chainrings 74mm BCD Black 28T, or say these Sugino Chainrings?  Is there any reason (beside aesthetics) that I couldn't move my current inner 36T chainring to the outer position?  If the change is possible, do you recommend any particular chainrings to look at?

I realize that I will have to shorten the chain and possibly shift the front derailleur.  Is there anything else that I need to be aware of?  Thanks very much for any help!
You’ll need a sub-compact (also called super-compat) crankset. With 110mm BCD the smallest chainring possible is 33 or 32 teeth.

There are sub-compact cranksets with 74mm BCD for the inner chainring and 110mm BCD for the outer chainring which should allow you to install something like 28/36. This Sugino OX2-901D Compact Plus+ for example. Looks like their smallest possible combination would be 24/34.

Keep in mind that a road bike front derailleur is not made for such small chainrings. Especially if you have a braze-on mount instead of a clamp for your front derailleur you could be limited in how far you can slide it down the seat tube.

Maybe a 33 teeth chainring combined with a 11–32 cassette would be good enough for you?