There's potentially 2 ways to do it:
1 - Using the "Post unRAR filter"
2 - Using the scripting interface to delete the files using a script you write.
To use the "Post UnRAR filter"
1 - Create a Filter profile.
2 - Use the filename accept/reject filters to add files to reject. For example I added "Bonus.rar" to the filename reject filter.
3 - In the autopar options, select this filter profile. ONLY Filename filters should be used for this.
[.]htm
[.]html
[.]nfo
[.]sfv
[.]srr
[.]txt
[.]url
bonus.rar
Is my list.
Is that it looks like after an unrar.
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter Bonus.rar
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter TOWN - NZB FORUM - KLICK IT.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter TOWN - NZB INDEXER - KLICK IT.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter Top Usenet Provider - CHEAP - FULL SPEED.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter Copy(1) of TOWN - NZB FORUM - KLICK IT.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter Copy(1) of TOWN - NZB INDEXER - KLICK IT.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter Copy(1) of Top Usenet Provider - CHEAP - FULL SPEED.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter TOWN - NZB FORUM - KLICK IT.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter TOWN - NZB INDEXER - KLICK IT.url
[08:05:36] HIGH HFC: Rejected RAR Filter: Filename Filter Top Usenet Provider - CHEAP - FULL SPEED.url
Is what it shows in the log.