Here is the part of the Rent Stabilization Code that addresses rent adjustments for capital improvements.
https://govt.westlaw.com/nycrr/Docum...efault)&bhcp=1
As you can see, it's rather complicated and the building owner must apply, and get approval, for any increase in rent.
Any "agreement" that you and the owner make could be meaningless in light of the approval criteria so make sure he finds out what his limitations are. I'm sure he will want to recover his costs over a very short period of time when the code may require otherwise.
Using Budwad's example of $10,000 in capital improvements resulting in a $20 per month allowable increase in rent isn't likely to sit well with the building owner who will have to wait 41 years to recover his investment.
You might have to pay for your own modernization if you want it badly enough. Or move to a more modern apartment which I know that NYers are reluctant to do because of substantial increases in rent.
My sister in Manhattan has paid for several improvements in the 20 some years she has lived in her apartment.

