Changing water

No. Fresh water = fresh supply of oxygen into the system, plus a stirring up of particals that are likely already settled into safe places for them to be.

What would be the reason for wanting to?

(I also know nothing about your boiler...)

I seem to remember reading somewhere that it's recommended every X number of years. I may do mine at the 10 year mark but not before.

In general, never is good, barring some huge error in chemistry. The system corrodes every time you put new water (with new dissolved air, which means new oxygen) into it. Some newer systems are starting to suggest a filter (needs to be hot-water rated) in the return line - of course that adds to the pump head, but presumably helps to aggregate "what comes out" in one location where it can be removed with minimal new water involved. I suppose a fanatical installation could use a filter that was in-line for a month or so after water additions, and then bypassed to reduce the pump head.

I am going to finally hook up my storage tanks tomorrow and am installing a filter head from an in line fuel filter and using a filter that I use on
my coolant filter in my truck which is rated for hot temps. I figure there is bounch of crap in those old tanks and I will run the filter for a week or so then check it and see
what comes out.

I would not drain the water out if there is no issues, I have seen many 50, 60, 70 year old boilers that have never had the water changed with no problems.

Spirovent dirt trap......... Or Caleffi etc. Having large pressureized storage tanks is a perfect trap anyway, any particulate in the water will settle out in there and not do any harm to anything in the system.

TS