Only run VLookup when all data is finished?

Workbook is about 5000 lines of 3 columns. A:C is original data, D is new data, vlook is matching A:D and giving B:C. If that makes sense.

Anyways, since I have a vlookup formula in 2500 rows anytime I make a change to the other columns excel wants to slow down and formulate. I want to be able to get all the data into place, and then tell the vlookup to proceed. I know I could delete the vlookup and then make changes but I am making this as a template for someone far less experienced than I am. So I need to keep it simple.

Another issue with it is that the data in G varies and may be 5000 or more rows on week and less another. So I have to have the vlookup continue down as necessary.