Yes, of course you can slacken the strings, you can do what you like, it's your guitar lol.
Try lowering the tuning by a semitone or whole tone, (one or two frets) then use a capo * on the first or second fret, which will bring it back up to "normal" pitch (EADGBE).
The capo will also hold the strings closer to the fingerboard, making it easier to play. Voila!
Don't worry about all the "rules and regulations", it's just about music, if it sounds right, it *is* right lol.
When I was first learning to play (over 50 years ago now) I had a guitar that was made by my cousin in the woodwork class at school, it was absolutely awful, but I was so obsessed with wanting to learn to play that I persevered with it (much to the amusement of all my mates, hahaha) until I got my first "real" guitar, 3 quid, brand new, lol.
*
https://en.wikipedia.org/wiki/Capo.
If you don't want to go to the trouble/expense of getting a capo, try using a biro or pencil, held in place with a strong rubber band lol. Just do whatever it takes to get a tune out of it, I wish you all the best with your endeavours, I still play almost every day :)