Hm... I tried the first in your original post and your updated, both give the same error. I check, and the file I'm using is definatly writable.

bash-2.05$ perl -ple "@f=split; for (@f[1..4]) { $_=1000 if $_>1000; }
+ $_=join(' ',@f)" TEST 
Can't modify constant item in scalar assignment at -e line 1, near "10
+00 if"
Execution of -e aborted due to compilation errors.

bash-2.05$ perl -lape "for(@F[1..4]){ $_=1000 if $_>1000 } $_=qq{@F}" 
+TEST 
Can't modify constant item in scalar assignment at -e line 1, near "10
+00 if"
Execution of -e aborted due to compilation errors.
[download]

Did I do something wrong?

-Jack C
jack {@} crepinc.com
http://www.crepinc.com/