Image append-string with special characters

I'm looking to produce a factory.bin image for the D-Link DIR-810L and Trendnet TEW-810DR.
The device pages presently use ncc_att_hwid, 32bit tool that is found in the GPL's source for either device.
The string duplicates the footer in factory firmware:

TEW-810DR^A^D1.1R^B^BWW^C^C1.0^E^G1.13B04 ^@^D^B^@)<8B>W9

In hex:

TEW-810DR..1.1R..WW..1.0..1.13B04 ....)..W9.

Examples of append-string from snapshot ath79/image/

append-string 00DB120AR9344-RT-101214-00 | check-size $$$$(IMAGE_SIZE)

append-string does not appear to take special characters and chokes on ")". Can someone point me in the right direction?