Resistor question

[radio nut]

So far when restoring a set you replace caps and out of tolerance resistors, check tubes and fire it up and see how it goes.
Every time so far at least a couple of resistors that checked ok as far as tolerance will float out of tol. once power and load has been applied for a while.
As soon as it warms up here in Ohio....and stays warm I will be working on one of those big Rca projection sets model 9pc41 (if memory serves correct).
My Muntz tv had about 20 or so resistor change value after10 hours or so of running it.

So, Am I being stupid if I am thinking about shot gun replacing of the resistors in the projection set that has 4 chassis's and 41 tubes and assorted parts?
Yes it will already take a while to get this set close to running let alone stable.
Just wanting opinions....