Nice, but there are size limits to the size of variables:
http://forum.mikrotik.com/t/the-maximum-size-of-a-read-written-file/167507/1
Until everything remains within 4096 bytes[1] you are fine, the issues may come with larger configurations.
Semi-random idea, but maybe you want to reset to the exported configuration without any changes to it and put a script to run at next reboot that sets that IP (and the other changes)?
http://forum.mikrotik.com/t/run-script-after-re-boot/157645/1
I.e. you reset the configuration, import the exported configuration from the other router, then reboot and have a script running once for correcting the IP(s) re-configured for the “spare” router?
This would imply two reboots, but I would be not so sure about the second reboot (after the configuration has been reset to standby.rsc) not being anyway a good idea.
[1] as msatter noted below, you can go up to 32768 and even much more using chunks on very recent Ros7 version (7.15)