How to assemble disassembled files

[Weininger Andreas]

I have the following problem: 

If I disassemble an object file on a DECstation 3100 with the help of
'dis', then the resulting file can't be assembled with 'as' because
'as' doesn't recognize some instructions like 'jr'. (I want to do this
because I want to instrument object files.)

Is there any other tool which can assemble disassembled files?
Please answer by email because I don't read this newsgroup.

Andreas Weininger
weininge at lan.informatik.tu-muenchen.de