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GENERALLY, lenders will lower limits only when the cardholder starts with risky behavior. There have been instances where some lenders have chopped limits due to having way too much available credit, but that's somewhat rare as long as you use the card at least a little bit.
Plus, look at the bright side: If you WERE to have your limits cut due to being unused, then obviously you're doing something right and not carrying a ton of debt lol.
I wouldn't worry; it most likely won't happen. I have an Amex with an 18k limit that hasn't seen a balance of more than 200 bucks in a LOOONG time.
Can it happen? Of course. All lenders occasionally CLD people for a variety of reasons. But to me there's not much point in worrying about these things because if it happens, it happens. There's not much you can really do to prevent it. If an algorithim decides you are worthy of a CLD than a CLD occurs.
I would just use the cards where/when they benefit you and try not to worry about it.