szurkebarat,
I know ingest puts some valuable info (like folder num and so on) into the images but I usually have to copy my memory cards to a mobile storage device and after shooting work with them on it. So it would be less space consuming - and perhaps faster too - to have PM's ingest optionally overwriteing (maybe using temporary files like it does renaming) the files stored on the storage instead of copying making it to be twice on the same device.
Is there such a solution or the only way is having the ingest or using a rename and add IPTC info but loosing other valuable details?
I'm not sure I fully understand what you're trying to do, but renaming does not change metadata in your images.
I think you just want to browse images on your mobile storage device without transferring them to your computer's internal hard drive? As long as your mobile storage device mounts as a disk, then you could just open contact sheets from it and work with the images directly. But I wouldn't recommend that since it sounds like those images are your only copy so if you accidentally delete a file then it could be lost for good.
If I haven't answered your question, please let me know.
-Kirk