"Text Manipulation -> Convert delimiters to TAB" could split one field
into more than one, but the delimiter has to be in the list ("@" is
"Text Manipulation -> Cut columns" from a table is similar, but it
not split on a "@" either.
"Text Manipulation -> Trim leading or trailing characters" could be
for this specific case, since you can trim off the end of a column
on a position (but again, not a specified delimiter). To prep for an
entire genome, you would need to break up the starting query so that
chromosome name lengths in any derivative queries are of a consistent
length, then merge back together.
Perhaps the "@" was just an example and one of these tools will work
you. If you are customizing, additions to the Tool Shed that expand
native tools are always welcome! http://community.g2.bx.psu.edu
Thanks for using Galaxy and for bringing up an interesting use case,