In the 5e ruleset, on the Inventory tab of the character sheet, there are two or four number fields with labels at the bottom left (depending on if you have the house rule for encumbrance turned on). The label control for the "Lift, Push, Drag" label (line 356 of record_char_inventory.xml) has no name and thus can't be altered using a merge rule.
Code:
			<label_fieldtop>
				<anchored to="encumbrancedrag" offset="8,1" />
				<static textres="char_label_encdrag" />
			</label_fieldtop>