I have a column of numbers which represent a change in value over the
previous year. I want to have a + in front of the number if it's a positive
change.
Let's say my first number is 500.

My problem is that I can write something like, if(a10,"+"&a1), but when
then I can't format the number.

If the number is in the millions I can't provide a comma as a thousand
separator and I cannot tell it how many decimal places I want to show. Is
there a really easy way to do that, or do I have to write a huge formula to
precisely spell out the formatting within the formula?