Custom `string` to `bool` conversion

Is it possible to register a custom `string` to `bool` conversion?

```
[ExcelParameterConversion]
public static bool? StringToBool(string? value)
{
value = value?.ToLowerInvariant();
return value switch
{
"true" => true,
_ => false,
};
}
```
I tried above with `bool?` and `string?` (4 combinations) but all of them fail with `#VALUE`

The request may come weird but I am working on drop down support for intellisense and for bool types when user types `TRUE` exceltooltip window also pops up. I couldnt find a way to properly handle it and I think I shouldnt handle it so I was trying to fill the value as `"TRUE"` so exceltooltip wouldnt pop and tab completion etc would work better