How to one switch between symmetry modes in space plane hangar

There are a few.

Wings provide lift and control, and having not enough makes you more vulnerable to shifts in fuel weight.

Thrust to weight is misleading, what is important is that you have enough force to move your mass not only against gravity, but against your aerodynamic drag. Most efficient, vertically launched rockets don't have this much trouble, but SSTO ascents try to get as much lateral velocity as possible while still in atmosphere.

Air Intake. A major issue with most designs, more air intakes will let you go higher and faster before beginning to burn precious jet fuel for the final ascent. 3 RAM intakes per Turbojet is generally acceptable, but very lightweight designs may be able to get away with 2.

The deathknell of every SSTO design ultimately comes down to finding a magic balance between your final altitude (Air Intake), rocket fuel weight to breach into orbit, and airspeed. Too much mass, your airspeed will suffer, but you may get higher with more intakes. Small SSTO's trade off mass for more speed (which slightly increases final altitude)

The last challenge is highly technical, but unique to every craft: piloting. The timing, ascent angles, and thrust controls make or break any design fit to see orbit. An avionics control module and good structural rigidity (plenty of struts, nothing should wobble, ever) will help immensely.

I know this is an old post but it IS possible to "undo" a quickload because I've done it before more than once with 0.20 and 0.22.

The key is to react as soon as you realize what you've done. In Windows, just hit Alt-Ctrl-Del and bring up the task manager, select ksp.exe from the processes tab and click on "End Task", this will kill the game. Restart the game and load your mission, then you will be at the point where your game last autosaved, before you did the quickload.

This works only if you do it quick enough, because a short time after the quickload mistake, the game WILL autosave again which will overwrite the persistent file, but it doesn't do it right away, and a quickload does NOT overwrite the persistent save file.

Again, I have done this more than once because I've made the same mistake, and I can tell you that it works.