If I understand your question you could either:
enter 0.85 in a blank cell and copy.
Highlight all cells to be "deducted"
Edit, Paste Special, Check Multiply.
Or by formula:
=0.85*A1, Drag as necessary.
Copy the newly pasted cells,
Highlight the original cells
Edit, Paste Special, Check Values
Delete the =0.85*A1 cells if desired.