The line you're looking for will be followed by something like this:
<maxFleetPoints>100.0</maxFleetPoints>
<fleetPointsUsed>95.0</fleetPointsUsed>
except the 95.0 will be replaced with whatever the current FP value of your fleet is. It's the only instance of <maxFleetPoints>100.0</maxFleetPoints> to be followed by <fleetPointsUsed>#</fleetPointsUsed>. And I mean the only instance of that with 100.0 between the <maxFleetPoints></maxFleetPoints>. There are many other npc fleets with 500.0 between the <maxFleetPoints></maxFleetPoints> that are followed by the <fleetPointsUsed>#</fleetPointsUsed> line.
Also, the value between <maxFleetPoints></maxFleetPoints> for the line you're looking for will always be 100.0 unless you change it. I recommend not changing it to 500.0 because that's the value most of the npc fleets use. Make it something weird, like 357.
The value you want to change appears to be the last instance of <maxFleetPoints>#</maxFleetPoints> in the save file, so that should help you find it if you search in reverse.
It was at 500 already (even though my fleet only had 100 max fleet points). When I tried to change it to 1000, nothing happened. Help?
That's because you changed the max FP of one of the npc fleets. The save file keeps track of the status and position of all the npc fleets, not just your own.
