Is there a way to change cells containing formulas so that they have
their current contents as literal values?

For example, if C1 was set to =A1+B1, and it was displaying 42 because
A1 was 27 and B1 was 15, I want to change it so that it's set to "42",
and will stay 42 even if A1 and B1 change.

I could click in C1, type "42", and press Enter. But I want to do this
for a range of cells all at once.

I suppose I could write a macro, but I'm hoping there's a simpler way.