Hello theandric,
It isn't possible truly to remove reverb that's been recorded into 'wet' sample sets, such as the MDA St. Eucaire. You can truncate its ranks' release samples by loading the organ via the 'Organ | Load organ, adjusting rank audio memory options' screen, which might (in moderation) help to some extent to give the impression that it's a bit less reverberant, but the reverb can't be removed from the attack/sustain portions of the samples.
The 'Organ menu: Organ loading settings: release sample truncation' section in the main Hauptwerk user guide has more details (page 78 in the current v6.0.2 version). Here's a topic (from 2017) that lists some dry sample sets (which have minimal reverb recorded into their samples):
viewtopic.php?f=4&t=16405&p=123280#p123280