Increasing temperature means increased kinetic energy on the atomic or molecular level. Temperature of a given substance is the average kinetic energy of the particles of which that substance is composed.
The temperature of a substance has no effect on its mass. UNLESS ... part of it evaporates and blows away, or melts in a puddle and runs off the edge of the table. As long as all of the substance stays there, its mass doesn't change, no matter how hot or cold it gets.
What happens depends on the temperature coefficient of the diode. If that diode has a positive temperature coefficient, it resistance increases with increased temperature. A diode with a negative temperature coefficient does the opposite.