This would not be considered "advertising," so I think you've got a lot more leeway in what you present. And in a non-advertising context, I don't believe you would be required to indicate whether a loan is fixed or variable, although I applaud your management for wanting to ensure customers aren't misled or confused.
Perhaps you could have some sort of generic message down at the bottom of the screen saying, "If you have a variable rate loan, the interest rate shown may be subject to change. Check your loan docs."
If that doesn't fly, you should at least be able to do something by loan product; e.g., all your HELOCs and all your credit cards are variable rate, or all your vehicle loans and all your home equity loans are fixed?
Sounds too simple, but it works for me. Good luck.
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The opinions expressed are mine and not those of my employer