Can I keep building obsolete units ?

[Pomphis]

As a matter of flavor, I would like to be able to continue to build Riflemen once Infantry is available, and Infantry once Mechanized Infantry is available for secondary duties like garrisons. I looked at CIV4UnitInfos.XML in the hope of finding when a units becomes obsolete and to change that. But I find only info about upgrades, so I wonder whether if I change that I can continue to build for example Riflemen, but no longer upgrade them to Infantry. Which is not what I want. Or am I looking in the wrong place, and obsolence is governed elsewhere ?

 

[Pomphis]

Just in case somebody else is interested: as was explained to me, units become obsolete once all their upgrades are available. So if one adds Mechanized Infantry as a possible upgrade for Riflemen, Riflemen will not become obsolete with Infantry, but only with Mechanized Infantry. If one wants to prevent a unit to become obsolete until Future Tech, one has to create a new unit with required tech Future Tech and make it a possible upgrade for all units one wants to keep non-obsolete.