how to relabel .iso ?
 

without re-mastering.

Clarification please! You can mount the iso using loopback and then change things within the iso. If you just want to rename the iso, a simple mv will suffice, isn't it?

I already know how to rename the file, thank you.
I needed to relabel the DVD. in the end I used Windows software to do it.

(didn't know loopback can write too.)

Still I don't understand what you mean by labeling! If you intended to change contents within the iso - then you can do that by mounting the iso using loopback. Just asking for clarification even after you have done the relabeling using a windows software.

Its the damn name of CD. Every time you burn a disc it asks for a name. Like 'MyDisc' is default in some CDburning software. Afterward, if you make and .iso image out of it, that name of CD is somewhere inside the .iso file, near beginning.

The term is volume ID.
An ISO-9660 is read only and so therefore will also be read only when mounted using a loopback device. There are some linux ISO editing utilities that I found with a quick qoogle but have no experience using them.

The correct linux approach should be mount the iso using loopback, copy the content to another directory, change the content as you see fit, and finally create the iso of the new content.

that's what I meant with the term 're-mastering'
I didn't want to 'rebuild' the entire (several Gb large) .iso file (which might change file order, etc..) just to change volumeID.

but perhaps it is not such an easy task, as Windows software also had to make new .iso

Here's how to do it: Install isomaster (apt-get install isomaster).

Isomaster is an easy to use graphical utility for editing iso files. Open the iso file in isomaster. Then click on File>Properties and you will see the volume name. Click on the volume name to edit it, then save. You will need to save it as a new iso file, but isomaster will only change the volume name to the one you gave it and not touch any of the other files or directories on the disc image.