Your screenshot shows Change Data Value, but because your question is about a lifecycle I would expect to see Marketo changing a revenue stage in a Revenue Cycle Model. Curious if you are changing data values to drive a Marketo RCM, or if you're simply tracking a lifecycle using only custom fields.
Either way, if you don't want the data value to change to MQL after field named "Changed Lead Lifecycle - TR" has a value "Customer," you can use a Choice in the Change Data Value Flow step that prevents it from changing to MQL if the current value is "Customer."