If the glass or nipple is not broken, the you can simply place the CRT socket on the tube as long as you line up the pins. The plastic housing on the ends of the neck only served to insure how the neck board goes on. After time, they become brittle and break.

If, when you power it up, you get blue lightning inside the tube, the vacuum is lost and the tube is toast.

Of course, straightening the pins may result in fracturing the neck and you will loose the vacuum.

No!

It is not safe to power it up without the neck board properly seated to the picture tube itself.

The manufacturer would use a blob of silicone to secure the crt socket to the neck. Unless you are really rough with your game, you shouldn't need anything to hold things in place. But, if it does seem to keep sagging due to the weight of the neck board, you can run a bead of silicone across the top which can be easily cut away if needed.

Apply the silicone AFTER securing the neck board on to the tube.

Not a focus issue. As mentioned, the shift in colors not lining up is a convergence issue. Not an easy thing to tackle via messages.

Convergence can be an issue of what direction the game is facing in regards to the compass (NSEW). But normally, someone has screwed with the purity magnets or dislodged the fixed positioning of the yoke.

If you take an in focus, straight down photo from the top showing the purity magnets ( the rotational fins located between the neck yoke coils and the neck board.) We might be able to advise some correction. But it more than likely will never be perfect.

But what you want to look for FIRST is if there are already white marks on the rings that might not line up any more. If they are there but not all in a line, you should put them back so that the white marks all connect. And that marking is usually placed at 12 o'clock.

This might correct the majority of the error.

Any silicone is fine. Your choice of color. They used both white and black back in the day (clear is fine too). You are not looking to weather caulk a window or anything. Just placing a flexible bead across it. For the cost of a tube, I wouldn't even bother with it unless I had some laying around already.

Degaussing is normally only necessary if the corners are badly discolored. And I mean a wash of the wrong color or a rainbow etc. Not just that the three color guns don't line up there (that's convergence and purity). This distortion is often introduced by powering up the game facing one way, and then turning it to face another direction. My normal suggestion to the people that work our arcade floor is to: Turn the game off, let it sit 10 minutes, move it to where you want, let it sit 10 minutes, and then turn it on. This allows some of the magnetism to diminish and it also allows the Auto-Degaussing circuit to cool off enough to provide another "Zap" to the coil upon next power up. You can also rotate the cabinet watching the picture to see if there is a direction where everything looks the best. Then, leave it there and follow the instructions above to move it how you desire it to stay.

Of course, the metal chassis can also be magnetized and sometimes the only way is with a professional degauss coil. Its rather hard to clear this kind of distortion by just using an Electric AC drill motor (a home brew degaussing coil). If you do have an actual degaussing coil, then go to town on it. If you haven't seen instructions elsewhere for using it, the technique is to power it up flat to the screen. Roll it around the screen in a swirling motion trying to cover all the territory. Ending by moving it to center. Back off with it still flat to the tube (and still powered). Once you get about 10 feet away rotate the coil to be perpendicular to the screen (90 degree rotation), and then turn it off.