File > Tempalte > Save template
Choose a Name that already exists within a Template Category and click 'Save', LO will promp you whether you want to override the Template or not. In case you choose 'Yes' it will append a '1' to the file-name of the Template.
I do not know if it's just me, but override implies to me to not change the file-name.
I can't confirm with
Version: 126.96.36.199.alpha0+ (x64)
Build ID: 48cfa0b00b22f11ade53aec79b2fdddad253e1bd
CPU threads: 4; OS: Windows 10.0; UI render: GL; VCL: win;
TinderBox: Win-x86_64@42, Branch:master, Time: 2018-10-03_02:01:42
Locale: en-US (de_DE); Calc: CL
*** This bug has been marked as a duplicate of bug 118755 ***