I have an Epiphone SG-400 and i like the power and feel I get from using Beefy Slinkies in standard tuning. Is it ok to use these strings in standard tuning even though the packaging recommends detuning?
Beefy Slinkys are optimal for down tuning. You can use them in standard tuning, but you must get your guitar set up for those strings. You might need the nut slots (especially the low E string slot) to be widened. The neck will need to be set up as well as the intonation and things like that. You won't ruin your guitar with Beefys in standard, just make sure you have these things done before trying. Hope this helps.
My Explorer came to me with baritone strings on it in .13-.72. Talk about some massive strings! Even in drop C it felt like playing with rod iron, and I am a fan of heavies.