Hi @MarwaTawfik,
Using a region specific classifier has been shown to improve classification accuracy by a bit, so I would recommend using this approach if you can. If you can't access resources to train your own classifier, then using the full length classifier is not that much less accurate either, and pre-trained classifiers are already available on the q2 resource page.
As for providing a new classifier, I haven't had to use those specific primers in some time so I haven't had the need to produce an updated classifier, and not sure when I'll get a chance to do it, however, since this is based on the Greengenes database, most local machines should be able to handle it. You can try training your own using the instructions here, which is what I used initially, or you can also use the RESCRIPt plugin also which has a lot more functionalities.
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