Yes, it is possible to resize MorphOS SFS partition. Just run the system from CD, use HDConfig to change (extend) the size of the partition (you need to prepare some space after the partition first), reboot, start system again from CD and use SFSDoctor to fix the resized partition (select it from the partition list, push 'Scan disk' button, then 'Repair' button and follow the instructions).
After reboot the resized partition should be fully usable again. Happy hacking! :)

PS. Me as well as The MorphOS Team takes no responsibility for any data looses. Make sure that you have made a backup of all important data first.

Would the resize with HDConfig make all the data to be erased?

I never tried it myself but the idea is to fix the partition size change after reboot via SFSDoctor and keep all the contained data ....
Data on a Partition immediately following the (then) resized partition most likely is lost after the change unless backed up elsewhere, though.


[ Editiert durch pega-1 an 2011/3/13 5:54 ]

HDConfig doesn't erasy any data on partition. It only removes the partition from the partition list. Let's assume you have the following layout:
Part1 | Part2 | Part3
and you want to extend Part2.
You need to first remove Part3 to make some space for extending Part2. First of course you need to backup all the data from Part3, because it will be overwritten (partially) by the extended Part2. Once done, just remove the Part3 in HDConfig and you will get the following layout:
Part1 | Part2 | Free space
Then you can change the size of the Part2 partition and extend it in HDConfig. It will warn you that this will cause the data to be erase, but this is a generic warning. You get the following layout:
Part1 | Part2 (extended by for example 2GB) | Free space
Then you should reboot and run the system from CD. Part2 partition is not visible to the system, because SFS detects that the size of the partition doesn't match the filesystem data. Now you can run SFSDoctor and fix Part2 partition and get access to it again.