initialize_all_variables should work to reinitialize a previously initialized var.
Just did this health check at 0.10
tf.reset_default_graph()
a = tf.Variable(tf.ones_initializer(()))
init_op = tf.initialize_all_variables()
modify_op = a.assign(5.0)
sess = tf.InteractiveSession()
sess.run(init_op)
print(a.eval())
sess.run(modify_op)
print(a.eval())
sess.run(init_op)
print(a.eval())
Result
1.0
5.0
1.0
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