When I tailweighted my racquet I put strips of lead tape at 1-3-5-7 like you suggested. First I removed the factory grip and I added the lead tape directly to the wooden handle and then I re-gripped it. The lead tape is really thin and you can’t feel it at all. In order to make the swingweight stay the same, the lead tape should be added right at the axis of rotation (or where the racquet pivots in your grip). I took a couple of practice swings and then marked that on the wooden handle.
I took off the end cap to look around any my racquet had some sort of plug in the hole there. I think that adding the lead tape to the wooden handle is a better idea than trying to shove it inside the handle or adding it under the end cap (which would increase the swingweight of the racquet slightly because the added swingweight is the mass you added times the square of the distance from the axis of rotation. So added mass below the axis of rotation also increases swingweight).
Right, it’s important to understand that you can’t make a racquet lighter or make it have a lower swingweight unless you REMOVE material. What you end up with is a racquet that has basically the same swingweight but a heavier static weight.
The idea in tennis is to help the racquet resist the momentum of the tennis ball by adding to it’s inertia. The balance of power is very different in tennis with a the ball weighing 5oz and racquets weighing 9-14oz. The ball literally pushes the racquet back when you return a hard hit (like a serve).
In badminton the birdie weighs 5g and racquets weigh 84-91g so the birdie doesn’t push the racquet back as much.
That said, I took a racquet that was 85g and 285mm balance unstrung and and 91g and 285mm when strung and overgripped and added 6g of lead tape to the handle. So now it weighs 97g racquet and has a balance of 268mm. When I play with it, it feels like the same racquet that it was before, but more so. It’s just as easy to move around for quick shots but I feel that I have a little extra power on those quick drives. And when I do attacking clears I feel like the I feel less resistance or impact from the birdie. The sensation is like I’m cleaving through the birdie. The effect is that I can hit it just as far with less effort. So in that sense the power of the racquet has been improved. It doesn’t seem to have any effect on my smashes though.
All in all I would call it a success and say that it is a pretty easy way to get an improvement in power (or lessened resistance from the birdie) without becoming head heavy or harder to maneuver. I’d just like to point out that I did this with a relatively light and easy to maneuver racquet.
If you tried the same thing with a racquet that was already maxing out your ability to maneuver then the extra static weight may make a difference. Caveat emptor. YMMV. IMHO and all that.