Question

First, foo is a Func<T1,T2,TResult> object.
Is is possible do something like

Func<T2,T1,TResult> bar = ConvertFunction(foo);

thus convert Func<T1,T2,TResult> to Func<T2,T1,TResult>.

Answer 1

Yes, that’s possible:

Func<T2, T1, TResult> bar = (t2, t1) => foo(t1, t2);

That basically creates another delegate with switched parameters that internally simply calls the original delegate.
This is the only way to perform this kind of “conversion” if you only have a Func<T1, T2, TResult> and not a Expression<Func<T1, T2, TResult>>.