I know this may be a little late, Jidai, but have you looked at the provided template by DCS? There are a few markings that are easy to remove and it is a true photoshop file so those markings are a layer all by them selves and can be removed simply by disabling that layer.
I suppose I could have provided a link. Sorry, didn't mean to be a jerk...
https://www.digitalcombatsimulator.com/en/downloads/texture_templates/fa-18c_lot20_template/