Regarding the tapes, I'm not too familiar with the Tenas, but I can describe how they usually work... I'm not sure how to describe it clearly without going step-by-step (in an annoyingly slow and detailed manner), so bear with me.
The usual design of such tapes (often called "second chance tapes" around here), is such that there are two layers. One is blue, one is white. The white is what's actually attached to the rear wings, while the blue is really just a sticker that's been placed on the white tape. You unfold the tape as one unit, blue and white together, exposing the sticky side of the blue part (to be clear, don't separate the blue and white parts, yet). Tape the diaper as you usually would.
If you need to adjust the tapes or take it off to use the toilet and put it back on, you can peel the white tape off of the blue part, and leave the blue part stuck to the front of the diaper. You now have a white tape. The white tape usually doesn't want to stick as well as the blue, but it'll work in a pinch. You can either tape it however you like, and put the white tape wherever you want (bearing in mind that you probably won't be able to remove it without tearing the diaper), or you can put the white tape directly on the blue part, allowing you to retape the diaper the same way that you originally did (this is useful when after using the toilet, for example).
If you're first putting the diaper on and need to adjust the tapes to get the fit right, you may not need to use the second-chance tapes (it depends on the diaper, and whether or not you burnished the tapes, pressed them firmly into place), but once a diaper has been taped for a while and needs adjusted, this is where second-chance tapes become useful, because the tape bonds strongly over time and can rip the front panel if you try to remove it.
The adhesive on the white tape will get a little weaker each time you retape, but having that blue sticker gives you a solid, tear-resistant surface you can use for retaping, so you don't rip the front of the diaper. It's like the landing zone panels plastic-backed diapers used to commonly have, only instead of one big one, you have four tiny ones that you can put wherever you want them.
I hope this description is helpful. It's certainly long, but I hope it's clear.