Modchip replacement

[BG]

1) Does the warranty cover a defective modchip (I'd hate to lug the thing there, only to be told modchips aren't part of the warranty package)?

This would depend on who you purchased it from....If there warranty will cover the chip or not....You need to get in touch with them and ask....(Of course the Warranty from Sony is void since you have a mod chip in it)

2) Since soldering a modchip to the PS2 is risky business in itself, would the replacement job risk doing any harm to my PS2 (in case the guy accidentally loosens something in there and the problem only manifests itself AFTER the warranty expires)?

If you really have to worry about this.....You need to find another installer.....A mod chip pro is not going to screw up the install or loose something inside.....