Some can, others cannot
if the 2 halves are spot welded or riveted together, USUALLY they can be drilled out and bearing replaced then bolted back together.
BUT, since those idler pulleys are so inexpensive on the
net and Tractor supply or farm home stores, its just not worth the effort.
Now the mule drive "V" pulleys are a bit more costly, but since usually by the time the bearings take a shit, the "V" in the pulleys now look like a "U" causing accelerated belt wear.
As "thrifty" as I am I will just replace them.
If you don't know, a needle syringe like a diabetic one will make a great injector
for adding grease to those bearings and making them last forever.
For over 60 years I've been injecting grease into implement/combine flange
type bearings keeping them running long past their normal life.
