Stably escaping an identifier

I am in a situation where I need to run dynamically generated queries with identifiers from an untrusted source. For example

SELECT * FROM <untrusted_table_name> WHERE <untrusted_column_name> = $1;

We can use format('%I', <untrusted_value>) to escape the identifier and avoid a security vulnerability, but if the provided identifier is already escaped, this introduces a problem. For example,

SELECT format('%I', 'my identifier');

returns "my identifier", but 

SELECT format('%I', format('%I', 'my identifier'));

returns """my identifier"""

because it is escaping the previously added quotation marks.

Is there a reliable way to determine if an identifier has already been escaped, or alternatively is there a function that will stably escape an identifier such that the identifier will not change if the function is called repeatedly?

Thanks,

Phillip