Not fully documented, but in the meantime you can try this script.
Then use:
LogicRun VARS "release=releasedate as ""D#YYYYMMdd T#HH:mm:ss"""
[[
COMMANDS
1,=return "$release$" != "" ? ("SetAttr MODIFIED=""$release$""") : ""
]]
Note that we're embbebing some Evaluator code to check if a releasedate is set. Otherwise do nothing for that file.