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I think it still counts as merit abuse. It's just that the motives are different. You aren't meriting yourself to rank up and participate in bounties, signature campaigns, giveaways, etc. You are only doing it to help yourself engage in regular forum activities easier. Like writing and replying to PMs without waiting for 24 or x hours to pass.
I think you should just ask to be whitelisted for free with your alt account to any staff member to lift the PM limit as what was mentioned in here -
New PM limits~
You are automatically whitelisted if you buy a
copper membership. You don't need to wear the copper membership, just own it. You can also be whitelisted for free by any staff member and a few non-staff, but we're going to need some reason to think that you actually deserve it. Do not ask me for free whitelisting.
Whitelisting is a not a license to spam. You will be immediately banned if you're found spamming, even if you bought a copper membership (and you will not be refunded).
For the 1 merit to alt account, well it is just 1 merit. I won't count it as a merit abuse as it is not like you're sending more than that, but it is best to say your intention through it through the Alts thread in Reputation, so that others will know.