I think you would be very safe. The withdrawal load and the shear load exerted by the weight of a guitar are well below safe values. If you want to have fun, use this online calculator to give yourself an idea of maximum allowable values.
https://www.engineeringtoolbox.com/w...ad-d_1815.html
And then if you want more go here.
https://www.fpl.fs.fed.us/documnts/f...chapter_08.pdf
Keep in mind the load is shared by multiple screws - the number depends on how you attach the strap.