It's not clear what you want. A construct like:

while (<>) {
    if (/begin/ ... /end/) {
        ...
    }
}
[download]

still reads the entire file, line-by-line. If your file consists of 'records' that start with ^lmo\d+, and end with the next occurence, playing with the range operator doesn't make much sense; you might as well do a straigth while (<>) { ... } loop.

What is it what you really want?

Abigail