If you go to the Insert->Names->Define menu, you will see that you cannot rename a named range. You can only delete the old one and enter a new one. This gets very, very annoying if that range is used in many places on a spreadsheet, because you have no choice but to manually edit each and every cell that used the old name. Note that LO already keeps track of each cell that uses a named range, just in case the range's value has changed.
impossible in 3.4.3 too REGRESSION from 3.3.4 works fine with 3.3.4 where you can rename without error maybe linked with https://bugs.freedesktop.org/show_bug.cgi?id=40909 crash when updating name's range
Will be solved in 3-5 with new range name dialog concept