How can I change dataset conditional on a function?

I have a vector of numbers. What I would like to do is to change the composition of this vector depending on which function I am using.

Let me explain it in more details:

% this is the vector I have

t = [1; 1; 1; 5; 5; 5; 2; 5; 5]
% Now let's assume I have two functions x and y that take t as an argument.

x(t)

y(t)

% I would like to write a code that says t equals to the vector you see above in function x
% while for function y every element = 1 in t becomes 6

Can anyone help me do it?

Thanks!