@CaptConfuzed
SOLUTION:
Little bit of guess work & a whole heap of luck later & I think I have what you need 
I manually created the folder structure & placed a 'DefaultRegions.xml' file here:
...Grand Theft Auto V\Plugins\LSPDFR\UltimateBackup\DefaultRegions.xml (correct? Made a guess)
& made the inside of the file look like this (just for testing):
<?xml version="1.0" encoding="UTF-8"?>
Testline01original
Testline02original
Testline03original
I then created an '.oiv' with just an empty 'content' folder (vital) & an 'assembly.xml' that looked like this inside:
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<?xml version="1.0" encoding="UTF-8"?>
<package version="2.0" id="{BC759B87-3DDD-4E96-A6BF-371863AF59D0}" target="Five">
<metadata>
<name>Test Replace Text String In xml File</name>
<version>
<major>1</major>
<minor>0</minor>
</version>
<author>
<displayName>a63nt 5m1th</displayName>
</author>
<description>
<![CDATA[Auto Installer Features :
---------------------------
• Automated syntax replace in "Grand Theft Auto V\Plugins\LSPDFR\UltimateBackup\DefaultRegions.xml" √
• No other game files or archives will be replaced or modified. √
→ Choose Game folder in Next Step!
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Changelog V1.0:
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Pure blind luck this
]]>
</description>
</metadata>
<colors>
<headerBackground useBlackTextColor="True">$FFFFFF</headerBackground>
<iconBackground>$FFFFFF</iconBackground>
</colors>
<content>
<text path="Plugins\LSPDFR\UltimateBackup\DefaultRegions.xml" createIfNotExist="False">
<replace line="*Testline01original*" condition="Mask">replace01test</replace>
<replace line="*Testline02original*" condition="Mask">replace02test</replace>
<replace line="*Testline03original*" condition="Mask">replace03test</replace>
</text>
</content>
</package>
=========================
I then ran the '.oiv' by double clicking on it, installing it with OpenIV & it successfully changed the contents of 'DefaultRegions.xml' to this:
<?xml version="1.0" encoding="UTF-8"?>
replace01test
replace02test
replace03test
Note: As the text I was replacing doesn't have any of the symbols required to be converted by the XML Escape / Unescape Converter I did not use it. You will most likely have to. Just don't forget about it
The '.oiv' I created will fail for the reason mentioned below if you try to run it on your setup but if you put the 'Testline01original' (01,02 & 03 etc) lines somewhere inside your 'DefaultRegions.xml' (make a backup first) & I have guessed the file structure correctly (easy enough to edit if not), you'll see the changes it makes
Extra:
One thing I did notice back in the early testing of this is that if the text string you intend to replace is not in the file you intend to edit, the installer will say it failed with an installation error. So you might want to warn your users of that Don't edit these lines ever, on fear of death etc.
If I remember right, even if it says install failed, it replaces what it can find & only really warns you that there was something that it didn't find & asks you to check the log. So not a complete 'nothing is installed, dead in the water' install failure, just a 'something wasn't quite right there. Make sure all the lines exist in the file' one .
Another observation I've made is that you want to make each line you may want to edit unique. So you can target only that line when you update & not have the '.oiv' replace 2 identical lines when you only want it to change one of them. The way your lines have a lot of variation in them it should be quite easy to select just one line but I thought I'd mention it as something to keep in mind for possible future projects etc.
I'm calling this a resounding success anyway. Never thought when I dropped you the initial message I'd get anywhere near a solution for you 
All that is required to do now is adapt the process to your specific needs. I'm confident I'll be able to help with that (now). If you have any trouble with it, just give me a shout
