Hi,
Don’t even try to undo what you have learnt over the past 20 years. You just need to accept the inevitable and realise that there are more up to date techniques to learn. Believe me, I have been through this exact same thing over the past few years and I came out the other end OK.
The one bit of advice I will give is NOT to assume that you know a particular aspect of programming when learning the .NET way of doing things. As an example, I assumed that I already knew how to access Databases since I had been doing it for years. To that end, I skipped the data access tutorials and went straight to development of my first .NET app. It took me about 3 months to create a fully functional Data Access Layer for this app with over 20K lines of code to do what was needed. It worked perfectly. When I had the time I then decided to go back and read up on what I had skipped in my .NET migration and the Entity Framework did in about 3 seconds what had taken me 3 month to write. Let's just say that the air turned blue for a few hours after that revelation.
Good luck with the migration.
Cheers,
Ian