Any appropriately rated (X/Y class) capacitor of the same capacitance and physical size can be used to replace the Rifa caps.
I tend to replace all the electrolytics as I showed in the linked video, there is only a few to replace and it can only help with stability and longevity. Just be sure to use good quality caps from known sources.
As for the carbon composite resistors, I was just about to have a look at that myself. The ones int he power supply sections could be replaced with equal rated metal films with no trouble, but if they are in the signal path somewhere, or have an effect on the reading of the signal, a recalibration/adjustment may be required after replacement.
Having said that, if they have drifted then an adjustment may be needed anyway, and replacing them with metal film would be a good idea (and maybe pull the meter back to being closer in spec, depending when the last adjustment was performed).
So the tl;dr of it all is: sure replace the carbon composites if you'll recalibrate/adjust the meter, or double check what the resistors are actually doing if no adjustment will be performed to check if they'll have an effect on your readings.