I will create a short derivative shadder that simplify some aspects of the implementation that i guess are the most relevant.
But, the fast go faster, so in plain english you may already put some correct context to the problem.
What i want, lets say, i have a simple 3*3 in size, ColorRect.
I just want to map the (0,0|0,1|0,2|1,0|1,1|1,2|2,0|2,1|2,2)coordinates of the image to a linear: 0,1,2,3,4,5,6,7,8.
IN that way, i can atribuite several tranformations in a precise way using shader logic.
uniform sampler2DArray texarr : hint_black;
textex = texture(texarr, vec3(UV, LINEARMAGIC));
And, then, i can map that using the sampler2DArray.
I was very happy when generic arrays come out, but only godot4. I think i can solve my problems using the already present sampler2DArray.
But, i need to map the UV to the Array index, in that case, using a simple nested 2-dimensional loop, as above stated.
The thing is i do not understand very well the uv and tranformations, i tryied brute force, but only get some cool moire efects
Like the 
results

That shows it is possible to make the dance going, but whats the correct move? haha.
The image shoud show, as my array is[red,green,blue], and in the case of a 4;4 image:
R,G,B,R
G,B,R,G
B,R,G,B
R,G,B,R
Can you easly understand the shadder needed to map to a n dimensional grid?
Sorry for putting my "homework" here.
Thanks for the support and eforts all you guys.