I have a cell with a drop down box with options "Yes" or "No". If "Yes" is
selected, is it possible to apply a format to OTHER cells? For example, make
the text or cell(s) grey to show that no input data is required for these?
Conditional formatting only applies the format depending on the value in that
particular cell.

For example:
Cell A1 has a drop down box, a choice between "Yes" and "No".
If "No" is selected, the user inputs data into cells A2 and A3, and cells A4
and A5 contain formulae.
If "Yes" is selected in cell A1, I want to make cells A2 - A5 grey to show
these cells should be ignored.
Thanks!