Is there a way I can do a loop in an excel formula?
Is is possible to call a macro on a cell change event?
Is is possible to modify or add formulas to Excel?

When a formula is updated, I want a loop to fire off that updates the value
of the cell by appending a number to it:
essentially I want to automatically change a column without manually running
a macro. For example, I want the formula to make sure the value in a given
column is unique, so I would want to change:
1
1
1
1
1

to:
1
1_1
1_2
1_3
1_4

Any help is appreciated...
thanks, dan