I don't see why not, as long as you don't delete the HBO Max channel app itself as that would remove it from your Roku account and thus remove it from both Rokus.
Seems to me that signing out from within the app and signing back in with credentials for different HBO Max account should only affect that one Roku. If not, you can always reverse the process and put it back the way it was.
[Edited to add ...]
I'm not sure if this is relevant, but are each of these HBO Max subscriptions through Roku, directly with HBO Max, or through some other 3rd party than Roku?
And for any subscription through Roku, is this viewed from within The Roku Channel or is viewed in the HBO Max channel app?
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