data validation and predict future costs

Hi

ive got a forecast spreadsheet and ive used simple formulas to predict future expenses for the next two years.

i need to be able to predict future costs quicker instead of changing formulas per line item.

i've completed 2018 & 2019 costs as per example as what i would like it to look like however not all cost categories use the same rates - see rates tab.

i would like to use different rates as in columns M&N in rates tab as well as different averages to predict future costs (see columns D thru G in rates tab as well)

and i've got a one-off cost in 2018 for global meeting that i need to forecast in Jan only - i assuming to simply add that value to Jan

does anybody know of data validation formula to simply change the values for future expenses more quicker instead of changing formulas per line item?

thanks