Cylinder replacement is probably due to eu regs which suggests that cylinders under 500cc aren't exempt from testing every 10 years.
This was from a post on target talk.
The initial certification of the pressure cylinders (considering most if not all are made in and sold in Europe) falls under directive 1999/36/EC (Transportable Pressure Equipment Directive) and must be marked with the π symbol and the notified body number.
Periodic inspection (which includes but is not limited to pressure testing) for pressure vessels is mandated by each country's legislation.
The periodic inspection is mandated by the above directive as well as ADR and RID (Directives 94/55/EC and 96/49/EC) respectively.
All of the above directives have been incorporated in the legislation of the EU countries.
Contrary to what is a common belief there is no lower limit concerning the volume under which certification is not required.
The 10 year thing comes from
"4.1. The notified body must affix its identification number or have it affixed to the transportable pressure equipment and draw up a certificate of conformity for the tests carried out. This certificate must be kept for a period of 10 years."
This European Standard specifies the requirements for periodic inspection and testing of seamless steel transportable gas cylinders (single or those from bundles) intended for compressed and liquefied gases under pressure, of water capacity from 0,5 l up to 150 l.
NOTE As far as practicable, this standard may also be applied to cylinders of less than 0,5 l water capacity.
There's now a company that does re certify small volume cylinders.
This was all from the outfall of the Issf rules which stated no bottle over 10 years can be used in competition. How a certificate and number shows that bottle hasn't been modified I don't know. What I do speculate on is how long it will take before this trickles down to flight checks or insurance. But then the USA can demand a cylinder is visually empty anyway at certain airports.
It maybe the days of custom cylinders are becoming more difficult but as I've said there's seemingly nothing a number can do to prevent a fake or adaption.
Of course air arms may have done it for a completely different reason.