I've downloaded several new fancy weapon and armor additions that have exactly the same stats as some of their equivalent vanilla equipment.
Therefore I'd like to adjust the stats - quickly if possible.

For instance, I'd like to raise the value of a complete weapon set by 5% and lower the whole sets weight by the same percentage. To achieve that using the CS only, I'd have to go through all 9 weapon parts of a certain set separately. It is a little easier through the weapon spreadsheet of tes4edit but still requires changing values individually.

That's why I'd like to know:

Is there any way of exporting a weapon spreadsheet to excel and then importing the changed data back to the esp?

Is there any other alternative that allows me to change the stats of a certain weapon set at once?

You can do it but it's only worth it if you want to tinker with the numbers repeatedly as setting up a spreadsheet with formulae etc is more effort than manually editing.

Anyway, in Wrye Bash you can right-click on the esp and select Export > Stats

You don't actually have to change the esp. Wrye Bash will import from a csv file when rebuilding the patch if desired - place your csv file in Oblivion\Data\Bash Patches\.

There's not a quick way to do this automatically, sorry. But for an example of the spreadsheet that wetblanket is talking about, check out the MOBS download page, http://www.tesnexus.com/downloads/file.php?id=28537. Corepc and I adjusted every one of those stats manually, within the construction set.

Thanks for the information @wetblanket & BFG99

Think, I'm gonna use TES4Edit then, seems to be the easiest method in this case.