Is the following a valid bitcoin private key? - FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFE
since the group is cyclic with order N, then this key will be equal to 0x14551231950b75fc4402da1732fc9bebd (your key modulo N)

&gt;&gt;&gt; hex(N)
'0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141'
&gt;&gt;&gt; y=0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFE
&gt;&gt;&gt; multiply(y)
(101611976893179986611445456504760352678020054910766426941542489291446644113297, 62728409327141118228093362610154100530630533850909349244575637074165425046447)
&gt;&gt;&gt; y%N
432420386565659656852420866394968145597
&gt;&gt;&gt; multiply(y%N)
(101611976893179986611445456504760352678020054910766426941542489291446644113297, 62728409327141118228093362610154100530630533850909349244575637074165425046447)
&gt;&gt;&gt; hex(y%N)
'0x14551231950b75fc4402da1732fc9bebd'