Yes, you can shrink/move/grow a root partition without any reboots (nor livecd, nor usbkey): consult this answer. It's very well written and easy to follow, although quite long and a little risky.
resize2fs can't shrink online
ext4 partitions. This limitation, when applied on the root partition may lead you to think you can't avoid rebooting the host to allow shrinking the
root partition, which might be something you want to avoid. The linked process will allow you to umount the root partition without any reboots. So in this light it is not strictly speaking online resizing in regards to the mounted state of the partition, however it remains an online resizing in regards to the network online status or reachability of the host.
Of course, if you only want to grow your ext4 partition, you should stick to the conventional working
The general solution I've linked will work on any type of dedicated or VPS solution for instance.
TLDR; this solution implies to
tmpfs so you can
umount safely your root partition live and fiddle with it. Once done, you'll
pivot_root back on your new root partition.
This allows pretty much any manipulation on the root file system (move it, change filesystem, changing it's physical device...).
I have personally used this, and it works very well on debian system also, but the guide was initially written in 2007 for redhat, the answer I've linked was updated for CentOS7. It's highly probable that it'll work on your OpenSUSE, although probably with some adaptation.