I dislike the "Advanced weaponry" ruins perk that upgrades your unit. Is there anyway via a mod or custom configuration to disable it and leave the other ruin perks intact?
You can edit the game files to remove this specific Ancient Ruins reward.
The data for the rewards is in a file called CIV5GoodyHuts.xml in:
C:\Program Files (x86)\Steam\SteamApps\common\Sid Meier's Civilization V\Assets\Gameplay\XML\GameInfo
Before making any edits, I suggest you make a backup. Then open the file in notepad/other text editor and remove the following values:
<Column name="UpgradeUnit" type="boolean" default="false"/>
<Row> <Type>GOODY_UPGRADE_UNIT</Type> <Description>TXT_KEY_GOODY_UPGRADE_UNIT</Description> <Sound/> <UpgradeUnit>true</UpgradeUnit> </Row>
shanondin's answer was helpful but didn't fully solve the problem. Starting from their solution I was able to find other places where the upgrade was referenced.
Rather than delete the reference in the XML file I opted to learn the mod tools and alter the game that way.