This is a oneliner that removes the AIX TIMESTAMP, and prepends the date:

$ errpt |perl -lape '@_=$F[1]=~/(..)/g; substr $_,11,11,""; $_ = ($.==
+1? "TIMEDATE".(" "x8) : "20".join("-",@_[4,0,1])." ".join(":",@_[2,3]
+))." ".$_'
TIMEDATE IDENTIFIER T C RESOURCE_NAME DESCRIPTION
TIMEDATE         IDENTIFIER T C RESOURCE_NAME DESCRIPTION
2013-09-30 15:27 982C78BF   T S mir0          DISPLAY ADAPTER CONFIGUR
+ATION ERROR
2013-09-25 16:27 BA431EB7   P S SRC           SOFTWARE PROGRAM ERROR
[download]

You can also replace the TIMESTAMP with the TIMEDATE:

errpt | perl -lape '@_=$F[1]=~/(..)/g; substr $_,11,11, ($.==1? "TIMED
+ATE".(" "x9) : "20".join("-",@_[4,0,1])." ".join(":",@_[2,3])." ")'
IDENTIFIER TIMEDATE         T C RESOURCE_NAME DESCRIPTION
982C78BF   2013-09-30 15:27 T S mir0          DISPLAY ADAPTER CONFIGUR
+ATION ERROR
BA431EB7   2013-09-25 16:27 P S SRC           SOFTWARE PROGRAM ERROR
[download]

for the following errpt output:

IDENTIFIER TIMESTAMP  T C RESOURCE_NAME DESCRIPTION
982C78BF   0930152713 T S mir0          DISPLAY ADAPTER CONFIGURATION 
+ERROR
BA431EB7   0925162713 P S SRC           SOFTWARE PROGRAM ERROR
[download]

</code>

Note that AIX errpt output does not have the seconds, so you can add those as hardcoded :00

Should you not have a header in the output you want parsed, then remove the $.==1? "TIMEDATE".(" "x9) :

Sorry for necroposting.