Power Query/ Get and Transform Merge Columns if then else combined

I have several rows of data with part sizes and specifications. I'd like to merge columns based on the value in the column. I'm hitting a wall building this out in a custom column in Power Query.

The "size" column can only be "large" or "small". If the column is "large" then I need only this value in the new column. If the value is "small" then I need "small" and the column values 1-7 when they are not equal to "N".

I've merged all column and then began manually replaces the values for "N" and but there's endless possibilities so I'm hoping for an easier conditional custom formula.

Attached is a sample of the desired results.