I would recommend using the “B” rate table found in the Costs tab of the Resource Information window. If you want to change all labor rates starting on your FY April, then go to Resource Sheet … and look at the Std. Rate and Type columns. Filter Type to Work (assuming that’s labor). Now, by changing your Status Date to a date after your Fiscal YE date, values in the Std. Rate column will reflect the rate change.
From the Res. Sheet, you can copy your “now” rates into Excel, make your changes based on a calculation or input, in Excel, then AFTER you change the Status Date to after April, copy the revised Excel rate column and paste into Std. Rate column in Project. Then you should save your Current Baseline into BL1 (if you haven’t already done so), and rebaseline those tasks effected by the rate change, and save to BL2. You can then compare the cost of BL1 vs. BL2. Hope this helps. I’ve used this technique to quickly change hundreds of resource rates for a 6 year period of rate escallations.
Please let us know how you finally approach this and the results you achieved! Best of luck! Angelo