[rexpress]

Just wondering if this is an example where you are looking for dynamic scope instead of lexical scope? E.g:

y = 1;

expression = Block[{y},1+y];

Print[expression]

2

There are also the 'formal' symbols, e.g. https://reference.wolfram.com/language/ref/character/FormalY... if you want a symbol that will never be assigned a value but can still be substituted using ReplaceAll etc.