SRX5308 checksum on updated .cfg

I have an ISP that (too-) frequently changes the IP address of client systems.  I often need to update the incoming firewall rules.  This can be done by manually changing each rule for each remote system, but since the config files are saved in ASCII format, I'd like to edit that file and re-upload it to the firewall.

But after doing so, re-uploading the file to the fire wall yields a checksum error on the 5308.

Is there a way to:

1) regenerate the .cfg file's checksum
2) clear the checksum so the firewall's firmware knows to regenerate it?
3) is there a tool that will recalculate the checksum on an existing flat file?

4) have the firewall rules use a hostname instead of a fixed IP address?

Updating many entries via the web interface is error-prone and time consuming.

Is there a later firewall similar to the 5308 that has such a checksum-updating ability  already implemented?

Finally, I suppose an existing utility such as expect(1) could interactively update configs via the CLI interface, but I was hoping this might be an already-addressed issue.

Thanks,

John