I have a large sheet with many duplicates.

I can't just run Remove Duplicates because I want to remove a specific
version of each, i.e. where a specific field value is either Null or Contains
specific text or has a value or < than.

Is there any way to use the Remove Dupes tool or a simple function that
would allow this?

Even more ambitiously I'd love to Merge them i.e. Compare one ore more field
values, if = merge ALL the fields, where both records have a value step
through and accept either/both.

Any thoughts? I am a newbie to functions and such but this seems like it
should be do-able.

Any thoughts appreciated!