Is the original values are #00, #03 and the checksum is #E5, then subtracting the original values gives #E5 - #00 - #03 = #E2.
With the new values of #02, #03, adding them back in you get #E2 + #02 + #03 = #E7, so you are correct.
For the past 20 years ParaDOS had the wrong checksum anyway, so I wouldn't be too concerned even if you do get it wrong, it will just annoy TFM's ROM Manager.