I went ahead and ordered the Axxess Auto Start/Stop Override Interface for GM 2016-2019 this morning. The 2017-2018 Regal is on the compatibility list, so I felt comfortable that it will work. Description says it keeps it disabled even after you turn off the key.
The Axxess part number is
AXSSO-GM and the MSRP is $186.00. I was able to get it from a Walmart 3rd party vendor for $109.00 with free shipping. It should be delivered by 8/31. I'll report back after I get it installed.
The Installation Instructions and Product Info sheet are attached.
**Note: The 2019 Regal is also on the compatibility list, but you have to use a different harness. It appears that harness is included.