Trimmer Capacitor/Inductor stability
As long as you don't bash it, an adjustable inductor or capacitor will maintain its adjusted value, being only affected by temperature.

Components that are intended to be long term stable will have a tempco specified for them. There are ranges of inductors and capacitors made with tempcos that will offset each other, so keeping the LC product nominally constant as temperature changes both. Your task is to read the data sheets to find matching types. Some types of capacitor are headlined as having 'compensating tempcos' in the data sheet, google can find them (capax, presidio, yuden ...)