How to set key value labels to BigQuery columns

Question

I know that in BigQuery we can set labels at a Table level as a form of Key:Value.

But how can we achieve the same functionality but to in a deeper level to the columns? Some workaround? Some other service from Google?

We want to perform, in a later state, processing based on the values of these labels.

A change in the names of the columns are out of the question because of business requirements.

Thanks in advance!