Move the porcelain sink to an outdoor location if possible.
How to grind ceramic sink.
As far as chipping just go slow and deal with what shakes out.
A ceramic grinder uses a metal aluminum oxide or similar grinding wheel this is a wheel that has sharp metal flakes of aluminum oxide glued to the surface much like sandpaper.
Personally i would try and get an old cheap sink of same the construction to give a few trials on.
Porcelain sinks seem to have a paradox about them.
One person suggested to get a dremel and cut away the rim from the retaining nut without removing the sink less work someone else suggested to take the sink out which means cut the sealant and caulk remove the wood holding the sink remove the piping and cut it with a tile cutter.
Install a porcelain tile grinding disc on an angle grinder.
Set a water filled 1 gallon milk container next to or above the hole.
Ceramic is a very hard material and you need special tools to grind it properly.
Use small grit for a more mirrored finish and larger grits 120 and up for rough grinding.
Start out very slowly with the grinder set on a medium speed until you can get a feel of how fast the tile will grind.
It will grind down a ceramic tile or object with precision.
If the porcelain is coating cast fe and the sink bottom is flat you might consider a mag drill.
They re durable and hardy but they crack easily at the first sign of a drill.
Place a plastic bucket under the hole you need to enlarge.
The good news is that drilling the initial hole is the most difficult and riskiest part of drilling into a porcelain sink.