Can I put the D'addario EJ32 Folk Nylon Strings on my Steel String Acoustic Guitar? If not, what can be my alternative? I haven't tried doing so and i'm scared since I might be wasting a pack of strings but I have seen people online do it already. Right now, I am using the D'addario Phosphor Bronze Light Gauge strings but I would still like a more mellow sound that the classical guitar would provide? What should I do?
Unless it has an adjustable truss-rod, I wouldn't.
The tension will be considerably less than steel strings & as a consequence the neck will start to drop backwards.
The action will probably already be too low the first day you put them on, & a fortnight later will probably be nothing but buzz.
Even with an adjustable truss-rod, you might find the action comes out too low, as the bridge & nut heights will have been cut for firmer, thinner strings.
As pointed out in comments - you may have difficulty in even getting them to attach. Nylon strings tend to tie on, steel have a ball-end.
IME you can put nylon strings on a steel string guitar, but not the other way 'round.
I have a 68 Yamaha with a bulged top from the tension of steel strings. I put on high-tension ball-end nylon strings and didn't have to change truss rod or action. It's rejuvenated the old guitar, and it sounds great.
One advantage is that the smaller tuners on a steel string make tuning more precise with nylons!
An issue might be that the neck could bow back due to lower tension, but a truss rod adjustment would address that.
I'm going to speak to a different point than others have made. The strings on a guitar are only a fraction of what combines to give a guitar its tone and character. Steel strings require a much more rigid guitar body and neck and the lower tension of nylon strings cannot be expected to activate resonances and tone in the same way that steel strings and higher tension in that same guitar body would. Most would simply choose to take the steel string guitar to the music shop and make a trade or to purchase a separate nylon string guitar and have one of each, but the final decision is yours to make.