conditional format problem

So a little more info is needed.  It depends on what is in column K, what you mean by "change" and if you are willing to use macros/VBA.

so formulas do NOT change the value in OTHER cells, they only produce a caluclation and show those results (but those results can 'spill' into adjacent cells).  So using formulas in columns K you can have something like:

=IF(F1>0, "TBD", A1)

and then if column F is > $0.00 then it will show "TBD" but if not is will show the value from A1

Since you say "conditional format problem" you could also change what you SEE in column K but not change the value using conditional formatting.  So you can create a custom rule on columns K (select column K, select conditional formatting, create new rule, use a formula to determine which cells to format) then in the formula bar type =F1>0

Then click format, go to number formatting, select custom, then in the 'Type' box type in:

"TBD";"TBD";"TBD";"TBD"

should look like this:

This will make any number or text show as "TBD" if the value in col F > $0.00 (note it will not change any errors or blanks).  Note that these cells will SHOW as "TBD" but the VALUE will not change to any calculation/formula using those cell will still be based on the VALUE in those cells

3rd option and most 'powerful' would be to use a macro/VBA but I will not type that here because I don't recommend it because IMHO it is limited and becoming less favorable to use VBA and not supported in web or mobile versions and not reliable if the workbook is shared with others.  But using VBA you could change the values or change the formatting.