Wouldn't it technically be insulated then?
Insulated or not insulated is irrelevent. The real issue is once you have the N/G seperated in the panel you are now either 1 puting neutral current onto the grounding conductor energizing the entire cabinet of the panel or 2 you have a peice of equipment that is ungrounded.
Seems solution could be as some suggested to put on GFCI like is allowed for other ungrounded circuits, insulating the bare neutral to prevent incidental multipoint loose, possibly arcing, contact to the grounded cabinet.
And as others have said If you can run a seperate grounding conductor you can run a new Cable.
The big issue I see often around here is several Generator installation companies are woefully inempt regarding the code and in effort to underbid the next guy will short cut installation related to code requirements and safety concerns. Biggest errors are related to N/G bonding location and existing panel revisions to seperate N/G. Running new 4 wire for the range and dryer can be costly and time consuming for the Gen companies that are trying to knock out as many installs as possible during a week.
Now if the Generator/ATS is indeed not a service equipment with the N/G bonding and overcurrent device on the ATS/Service connection then nothing internally to the panel has or has to change, but that actual scenario is rare for residential gen sets out there that are whole house setups.