If I'm understanding correctly, the problem is that you want to hurt low level monsters without killing them, or something similar. I've had this problem with levequests, when you do the initial quest to unlock leves for a specific zone.

The problem is that even a single piece of level 70+ gear is overkill for mid-ARR content. The stat boosts are too high. So all you gotta do is make a separate gear set of the same job for situations like these.

Wear all statless, level 1 gear. Most glamour gear is perfect for this purpose. For the weapon, use a weathered weapon or something similar. Believe it or not, your inherent character stats (the stats you have even without any gear) will make you rather tanky all the way to like level 45, but the damage you do will be very low. It's perfect for this purpose.