The short answer is no.  Generally speaking, unless your structure is unmodified (in which case, why not use the original file?) there is no way to write a standard-conformant PDB file while preserving original serial numbers.  Let's say you opened a structure, added hydrogens, and wanted to write it out with unchanged serial numbers.  Well, the hydrogens are going to have serial numbers larger than any heavy atom, so since they will be written along with their residue-mates in the file (else TER card conventions would be violated), the serial numbers will not be... serial.

Nonetheless, I can imagine scenarios where you would be willing to ignore the not-strictly-legal nature of such a file, so I'll add a feature-request ticket to the Chimera Trac database with you on the recipient list.  If anyone else would also like to be on the notification list, send me an email...

--Eric