Can we clarify something here?
Is her issue with cycling, or TRT? There's a pretty big difference not only from the wife point of view, but from the nurse point of view as well.
If it's TRT, then she should understand that symptoms can occur in subclinical areas that don't necessitate treatment, and that testosterone is needed for longevity.
Fact: Low testosterone can and will kill over time.
If this is about cycling; you're going to have to work with her on it. I don't recommend trying to "sneak", as men our age just don't need to do that any more. You have the ability to rationally explain your situation, desires, and viewpoint. Engage with her in a civil discussion; taking great care not to raise your voice, no matter how upset you're getting. Try to come to a compromise.
I promise, working on a way to meet her in the middle will carry with it far better results than getting caught defying her.
My .02c