It’s not so interesting I think.
They’re basically just taking equations of the form f(x,y)=k where k=0, and asking “ah but what about when k!=0”?
Indeed, looking at the constant as a variable by looking at the equation f(x,y)=z IS quite useful. (I’m reminded of Feynman favorite trick for solving integrals). That generalization trick is actually useful in MANY contexts. But there’s nothing novel here.
The same trick is used in f(R) theories, where the Ricci scalar in General Relativity is replaced with a linear function. https://en.wikipedia.org/wiki/F(R)_gravity
Reminds me of TRIZ methods too, trying to find assumptions or constraints and playing with variations of them.
So yeah, nothing novel here.