How to use the slider to avoid keyframes movements?

Question

Hi there,
first of all, I have to tell, I am not a English speaker, so please excuse me in advance. Anyway, I want to solve this particular issue: I have created an After effects project, where you can add into the composition your own text, logo or whatever... what the after effects project does is, that it turns your text, or logo into the 3D metal result. There is also camera cretaed, which moves from one position, to another. Take a look:
The inputed text is "add content" (I have 4 cameras alltogether, but I am showing an example just on the first one, so you will not see the whole text. The rest of the cameras are also in other compositions)
Here you can see the exact movement of the camera. However, if somebody inserts a logo or a text, which has for example 7 letters (in the next picture it is just "content") it will look like this:
here you can see how big space we have. Also it is not appropriate to change the original size of the text in the composition to achieve the smallest gap, as we can see here. The height will be huge then...
If I would edit it by myself, I would do this:
-I would clicked on the button "2 views" and choose view from the "front"
-Then I would select all the keyframes and after that i would go into the left window "front" and  using the mouse I would draged whole the camera to the position I want:
The great thing about this is, that as I selected all the keyframes and then set the red line on one of them, the camrea will work even for the beginning! So this is how it will look after the fix.
What the problem is, that after the small edit I want to send this project to few of my friends. Then they can easily put their text, or logo in. The text will have different height, width...it will be shorter or longer. I was just wondering, if you could help with some expressions, linkings and so on, so in the final result, of one my friends could move with the  whole camera (not just with one keyframe) using the SLIDER CONTROL. At least for the x and y axis, if z axis is also possible, it would be brilliant. It also doesn't matter how many sliders there will be .
So basically with using the sliders, they should achieve this:
So i need some helpful steps. Please help me. This is very important for me. I will be so much thankful!! Really! (Thanks for the potential help )

Answer 1

You are way over thinking your problem and potentially headed down a path that will cause more problems that it will solve.
If you have a camera path that is already animated and you want to change the position of the camera path as a whole the easiest way to do that would be to create a null and then parent the camera to the null. Move the null and all of the camera movements you have set up will follow. No expressions are needed. This is the easiest way to change every aspect of a motion path, rotate the entire path, scale the path, or move the path on any axis.
If you really want to use 3 position sliders to move existing keyframes to a new value adding value + expressions values will allow you to do this. Just add an three expression control sliders to the camera layer (or any layer like the null you are using as a parent) select the name of the slider in the ECW and press enter and rename it. Something like this will be the result.
Notice that I also have rotation and scale controls in this setup. Now that you have 3 sliders you can separate the position property of the null into individual values enable expressions in each property and type in value +, then use the pickwhip to drag from the X value to your slider named xPosition (in my example) and repeat for each operation. The value + will add the value of the slider to the current value of the position keyframes. The expression will look like this for X:
value + effect("x position")("Slider")
If you want to use sliders I would use a null, add expression controls to the null for position, scale, and rotation, keep the camera position property unified and then use your expression control sliders on the null to modify your existing path. I would not suggest doing this directly on camera position with separated X, Y and Z values because this will change the shape of your camera path and would be more difficult to control. You'll probably also want to create a camera POInull and use this preset to tie the camera's point of interest to the null.
Here's an animation preset you can apply to a null that will give complete control to the motion path of any animated layer you make the child of this null. Search Animation Preset in the After Effects Search Help field if you do not know how to use them, create them, and save them.
As a final gimme, here's a CS6 project using this animation preset to control a null's position that used to change an animated camera path.