The only option is to export "Full answers".
Why does the export feature "convert Y to" only lets me enter a single character?
Because this is thought to convert multiple questions.
LimeSurvey stores "selected" as "Y", "not selected" as "".
But analysis tools (like SPSS) require a different coding. So you can convert to codes like "1" and "0", "1 and "2", or whatever you find best for your analysis.
Now my opinion.
You should not use any of these predefined question types. They are really outdated. There are better and more flexible ways to display them, e.g. "bootstrap-buttons"
Only the 5-point-choice might be usable - if you want to display as star rating.
Joffm
On the other side it is really easy to do a "Search&Replace" in EXCEL to get the desired codes.