Damn this used to bother me for so long but it was too advanced stuff to mess with at the time. Now thanks to your incentive and some acquired experience I'm able to easily learn it but my base/vessel setup solved that problem in the meantime. Anyway here's how to do it:
Open "Piratez_Globals.rul" inside "\XPirateZ\User\mods\Piratez\Ruleset" and goto "type: STR_STARCON_AIRCAR_RACE" string. Bellow "allowedCraft:" add your desired vessel string. To learn what vessel uses which string you can visit
online pedia, click on vessel and learn of its string from the address bar. Another way is from local "en-US.yml" language file.
Be aware of one thing though: the map may not support the craft you land with. Either too big or it don't fit the title set or whatever. If it crashes try a different vessel. You will also have to make the same change everytime you update the mod, or make own personal sub-mod that overrides official settings. And you can easily learn how from existing examples that come with XPirateZ.