Hi,
I have 2 problems, that would appear to be utter-basic, but I cannot find the answer anywhere, so apologies in advance for if this is too simple for this forum.

Problem 1:
What i'd like to do is this: copy a formula with a formula.
Example: Let's say there are these cells:
A1: 2
A2: 1
A3: =A1+A2
A4: .......

What i need is a formula that copies the formula in A3. NOT the value.
The reason for not wanting the value but the formula is that I want to substitute something in the formula, therefore i need a formula that copies the formula, so that I can then do a substitute on it.
The reason I do not want to manually copy-paste the formula, is that my data and formulas will change over time. E.g. if A3 becomes '=A1-A2' instead of '=A1+A2' in the future, I want that change to be reflected in the formula in A.

All I can find is the regular '=A3' formula, which copies the value in A3, and guides online for manual copy-pasting. Any help would be much appreciated.

problem2:
Problem 2 is a lot like problem one, except I need a formula that does what a manual copy-paste does, wherein it changes the relative references in the formula. So e.g. when I would copy-paste cell A3 to cell A4, it would change the formula to '=A2+A3', because the references are relative and without the $-sign. I need a formula that performs this copy-paste.
Same reasons as above for not manually doing this: the original formula might change, and when it does, i want this other cell to change with it.
As above, any help would be much appreciated.