MSDN

under the provider support for ADOX section of this document you will see that append and delete methods are not supported for ODBC.

however, the DAO.TableDefs.Append method in DAO 3.5.1 or greater, will accomplish that task. I haven't tested it .. but its listed in access as a supported method.
UNTESTED

use Win32::OLE

my $app = Win32::OLE->new(Access.Application);
my $table = Win32::OLE->new(DAO.TableDef);
$app->OpenCurrentDatabase(xxx.mdb);

#Returns the DAO database object
$database = $app->CurrentDb();

$table->CreateField(myField,Text,255);

$database->TableDefs->Append($table);
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Hope this helps.