Can you provide stan with data to be included in each step of the chain?

Is there some way to inform the chain at each step by adding data together? For each chain, I want to add a vector of data to another vector of data.
For example, I would do a for loop when using MH.

data {
int nsteps;
vector[10] y;
  matrix [10, nsteps] x; 
} 

model{
for(i in 1:nsteps){
y = y + x[,i];
}

You may run the same instance of Stan program consequentially by updating the data and the priors from previous runs. I am not sure about purpose of this exercise, though

I’m not sure whst you mesn with step.
If you mean iteration, then no, Stan does not have information about the current iteration number accessible.