val = '<s>'
idx = [val] + df.index.drop(val).tolist()
print (idx)
['<s>', 'noun', 'verb', 'Adj', '<end>']
print (df.reindex(idx))
col1 col2 col3
index
<s> 9 6 5
noun 1 1 1
verb 4 6 1
Adj 5 1 3
<end> 0 0 0