XBEE-PRO XB09-DP Firmware version 1002 Hardware version 1B42
The 16-bit Destination Network address present in TX Request (0x10) and AT Remote (0x17) packets appears to be completely ignored. It definitely does not have to match the ID register contents.
Example (ID in each modem = 2BAD) Test is with a pair of modems.
Sent: 7E 00 19 10 01 00 13 A2 00 40 53 86 E2 2B EE 00 00 48 65 6C 6C 6F 20 77 6F 72 6C 64 E9
Rcvd: 7E 00 07 8B 01 FF FE 03 00 00 73
Sent: 7E 00 19 10 02 00 13 A2 00 40 53 86 E2 AB AD 00 00 48 65 6C 6C 6F 20 77 6F 72 6C 64 A9
Rcvd: 7E 00 07 8B 02 FF FE 03 00 00 72
Both 0x8B (TX status) report success but give FFFE as the 16-bit Network Address of the responder even though 0x2BEE was used in the first TX and 0xABAD was used in the second. Note that it also reports a retry count of 3 (subject of another thread)
So, it is possible to use the Network Address field of a TX Request packet (0x10) for your own purposes. That may or may not be wise because a future firmware update might make use of this field.