Can a Potentiometer RV4LAYSD503A 50K Ohm 19-8351 be replaced with RV4LAYSA503A Potentiometer 50KOHM

I don't know but the similarity in part number would suggest one is a revision of the other or originates from a different manufacturer.

If they are dimensionally similar it would be worth a try if the correct replacement isn't available. The main thing to watch out for could be differences between the tracks of the two types.
There are four types of carbon potentiometer tracks; linear, logarithmic and anti-clockwise versions of those two. Linear types tend to be used for adjusting voltage whereas log types are about sound. Used for volume controls they closely mimmick the logarithmic response of human hearing.

The difference is easily recognised using an analogue ohmmeter.
Fitting a linear in the place of a log type would likely mean most of the adjustment would be bunched at one end of the track.

Although manufacturers tend to give spare parts of their own products fancy part numbers, very few are specially made and most are sourced from catalogues of generic parts. It is often cheaper to take a look in constructor catalogues and those supplying parts to the repair trade before resorting to manufacturer's spare parts.