No, you have to set them again. About the flight id you can change it as you prefere.
However if you use the same payload file, you'll have the same pax waiting, and the ZFW will then depend on the fuel settings. So, first time load for example about 45% of fuel 135 pax and front and rear cargo to the best zfw. Write all this values somewhere, change the Fsp Flight ID as preferred and go back to mcdu. Set every value and get the v-speeds, start fsp flight and set all values as saved on your paper (or wherever you've copied them) plus the v-speeds got from mcdu. I know, it's a little complicated, but it's the only way
However if you use the same payload file, you'll have the same pax waiting, and the ZFW will then depend on the fuel settings. So, first time load for example about 45% of fuel 135 pax and front and rear cargo to the best zfw. Write all this values somewhere, change the Fsp Flight ID as preferred and go back to mcdu. Set every value and get the v-speeds, start fsp flight and set all values as saved on your paper (or wherever you've copied them) plus the v-speeds got from mcdu. I know, it's a little complicated, but it's the only way
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