How to change small chainring
Most drivetrain setups have a 16 tooth difference between large and small rings. 


Near compact: 52/36
Compact: 50/34
Sub compact: 48/32 


You are trying to get a close to a super compact on a 110mm BCD and will have a chainring tooth difference of 13.

That means the rear derailleur will easily accommodate this as you have calculated.

The front derailleur will also handle the chaining size difference. 

Chain length is set on the large chainring and largest cog sprocket, so you should not have to shorten the chain (assuming your chain is correctly sized to begin with). You will be within the derailleur total capacity so it will take up the extra slack. 

If you do have too much slack in small ring and smallest sprocket, check the chain is sized properly.