to the forum oilfieldcowboy (& family) and congratulations on your new Cougar.
There shouldn't be a problem opening the slide-out a bit for access, as long as the trailer is towing fairly level. If the trailer is several inches nose-high or nose-low when hitched to the tow vehicle, then you should re-evaluate & adjust your set-up. As close to level as possible is best.
I see (from the Keystone website) that you have the short bedside shirt closets... I would suggest, instead of cutting the bottom out of them
that maybe you could modify the upper portion of the pantry (next to the frig) and add a bar for hanging longer clothes. I'm not familiar with the pantry in your specific model, but some RV's have that pantry/wardrobe with an optional hanging bar & adjustable shelves below... maybe this would work for you too.
Some folks add wire shelving to the bedside shirt closets & simply fold/stack tshirts, shorts, jeans, etc.
Other ideas -- look for creative ways for better use of empty space (as long as it doesn't compromise the integrity of the structure). Add a small 3-4 hook coat rack (inside) at the end of each bunk for children's jackets, pj's, special blankets, a small mesh (garment/laundry) bag to hold toys, etc. If you don't already have storage drawers/doors in your dinette booth, you might consider adding those for pantry/kitchen items.
Another common modification is to add easy-access doors (with storage baskets) or drawers below the main bed or bunks... of course that depends on the amount of open/usable space.
Check the "Modifications" section of the forum... several members have posted info/photos & good ideas.
Hope this helps,
Terri, the Chevy co-pilot