I don't know whether it helps or not....
Put this in config.xml...

<?xml version="1.0"?>
<config>
    <modules>
        <MyModules_XMLoverrides>
            <version>0.1.0</version>
        </MyModules_XMLoverrides>
    </modules>
</config>

Put this in systems.xml...

<?xml version="1.0"?>
<config>
    <sections>
        <carriers>
            <groups>
                <ups>
                    <fields>
                        <unit_of_measure>
                            <show_in_store>1</show_in_store>
                        </unit_of_measure>
                    </fields>
                </ups>
            </groups>
        </carriers>
    </sections>
</config>  

Put this in MyModules_XMLoverrides.xml

<?xml version="1.0"?>
<config>
    <modules>
        <MyModules_XMLoverrides>
            <active>true</active>
            <codePool>local</codePool>
        </MyModules_XMLoverrides>
    </modules>
</config>  

This might set the scope at store level.
Not tested. Try at your own risk :)

I don't know whether this helps or not....
Put this in config.xml...

<?xml version="1.0"?>
<config>
    <modules>
        <MyModules_XMLoverrides>
            <version>0.1.0</version>
        </MyModules_XMLoverrides>
    </modules>
</config>

Put this in systems.xml...

<?xml version="1.0"?>
<config>
    <sections>
        <carriers>
            <groups>
                <ups>
                    <fields>
                        <unit_of_measure>
                            <show_in_store>1</show_in_store>
                        </unit_of_measure>
                    </fields>
                </ups>
            </groups>
        </carriers>
    </sections>
</config>  

Put this in MyModules_XMLoverrides.xml

<?xml version="1.0"?>
<config>
    <modules>
        <MyModules_XMLoverrides>
            <active>true</active>
            <codePool>local</codePool>
        </MyModules_XMLoverrides>
    </modules>
</config>  

This might set the scope at store level.
Not tested. Try at your own risk :)