Probably not in one go.
4-part names can dealt with Converter>Filename-Tag:
%artist% - %dummy% - %dummy% - %title%
and 5-part names with
%artist% - %dummy% - %dummy% - %dummy% - %title%
But why do you throw away already existing information. I would import all of it.
It is very hard in the end to assign the correct album and track if you only have the artist and title.
if you want to assign the data to fields, you have to use the different patterns.
If you only want to mdofiy the filename, you can use an action of the type "replace with regular expression" for _FILENAME
Search string: (.?) - . (.*)
Replace string: $1 - $2
As you said:
(.?) -
means: take the first bit up to a hyphen in a non-gready way (which is the ?) and save it in a variable.
. -
means: take anything in a gready fashion
(.*)$
means: take anything that is left after the last hyphen as the gready expression before has gobbled everything up and store it in a variable.
$1 and $2 then refer to that what you find in the 2 blocks in parenthesis.