It might be ok, but it's not always a straight swap. Coconut oil is 100% fat, and butter is only about 80%. It means you might need to up the quantity a bit to get the best texture.

Without seeing the tree or needles it's really hard to say. As long as you are sure it is a pine tree and the needles are edible then I'm sure a spearmint kind of flavour would work.

That makes perfect sense. I'll make sure to chill my coconut oil first, then, immediately chill the dough before handling next time, because I will certainly be making them again! My boyfriend just ate 3 cookies in about 10 minutes! I really appreciate your quick response, I just love your blog!

I totally agree about it being fairytale like to go foraging for pine needles. It really adds to the experience. Much better than just going to the shop!
Sorry you had melting issues. Coconut oil does have a low melting point (much lower than butter) so if the oil isn't really cold and hard before you start, or if the dough is mixed a little too much, or handled a lot with warm hands or made in a warm heated kitchen, or near a warm oven, it will get really soft. There's no getting away from that. My kitchen is always pretty warm so I usually stop once the dough is made and refrigerate it for 20 mins or so then roll it out and cut them once it's cold. I have added a note to the recipe about that in case anyone else has issues. So glad you enjoyed them regardless though!

To get the best shortbread texture it really needs to be a hard fat that is used so either coconut oil or vegan butter. Liquid oil won't give the same texture. I also don't think they would taste quite as nice with vegetable oil. You could try with one batch and see what you think before making them for gifting. I have no idea what quantity of liquid oil you would need as I haven't tried it so I can't help with that I'm afraid. You would need to add just enough to make a dough. Let me know how it goes!

Thank you so much for including me Francesca!