Is there a way to keep a pattern on the ground and remove the pattern from my design inventory without the pattern being changed or removed?
You'll want to stop by the Able Sisters' shop and talk with Mabel.
She'll let you copy/move your designs over from your 8 personal slots to a bank of 72 slots.
The only limitation with moving/coping your patterns over, is that you'll need to talk to her again to move those patterns from her back to you. Likewise, you can't use any patterns if Mabel is holding onto them. (As in, wearing a hat or shirt made with your pattern will become "blank" when the related pattern is stored away.) Just Copy/Move the pattern back when you want to use it again!
Note: If 72 slots isn't enough, you can also save patterns as a QR Code! The only restriction though is that a QR Code pattern is locked and cannot be edited or shared. This is great if you want to save something for the sake of it, without taking up space. (assuming you're ok with that pattern being stuck like that permanently.)