In reality this, as said before, is a CYA for the manufacturers. I am more than familiar with old insulation falling off in my hand.(my house 1930.s for one, along with many I have worked on)
In my case when we redid the house we used antique fixtures. Being that the only code problem here is "follow the manufacturers recomendations and there was none, I simply took all precautions that could be taken dealing with old wires.
This type work (without the 90C problem at hand) is one of the most frettfull task we have to deal with ie, wondering if by moving these wires around in the box actualy caused problems upline that we couldn't see.
This type work is dangerous enough for the seasoned pro, much less the DIYer.
On the otherhand if he is being coached through a project (books, family electrician, neighbor, or friend) that is simple enough,
there should be no problem.
Roger
