Hexedit the status.dat file in the savegame folder. Find the name of the plane, then using the first character of the plane name as a reference, add 30 to the offset (e.g. 1130 ---> 1160). The following string is the number of hardpoints on the chosen airplane. Each value takes up four bytes.

03 00 00 00 01 00 00 00 means 3 hardpoints on the left wing, 1 on the right. Edit as you wish.

Then add 70 to the initial offset (1130 ---> 11A0). That's the armor level of the plane. E.g.

0A 00 00 00 0A 00 00 00 0A 00 00 00 0A 00 00 00

That means 10 armor on each slot. Change it all to FF to be invulnerable to just about anything but crashes.