modifying softmax function in tensorflow

Question

I started using tensorflow about a week ago, so I'm not sure what API can I use.

Currently I'm using basic mnist number recognition code. I want to test how recognition precision of this code changes if I modify the softmax function from floating point calculation to fixed point calculation.

At first I tried to modify the library but it was too complicated to do so. So I think I have to read tensors and modify(calculate) it in the form of array and change it to the tensor using tf.Session().eval() function. Which function should I use?

from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)

import tensorflow as tf

x = tf.placeholder(tf.float32, [None, 784])
W = tf.Variable(tf.zeros([784, 10]))
b = tf.Variable(tf.zeros([10]))
y = tf.nn.softmax(tf.matmul(x, W) + b)
#temp = tf.Variable(tf.zeros([784, 10]))
temp = tf.Variable(tf.matmul(x, W) + b)
#temp = tf.add(tf.matmul(x, W),b)

y_ = tf.placeholder(tf.float32, [None, 10])
cross_entropy = tf.reduce_mean(-tf.reduce_sum(y_ * tf.log(y), reduction_indices=[1]))
train_step = tf.train.GradientDescentOptimizer(0.5).minimize(cross_entropy)

init = tf.global_variables_initializer()
sess = tf.Session()
sess.run(init)
#print(temp[500])

for i in range(100):
  batch_xs, batch_ys = mnist.train.next_batch(100)
  sess.run(train_step, feed_dict={x: batch_xs, y_: batch_ys})

correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
print(sess.run(accuracy, feed_dict={x: mnist.test.images, y_: mnist.test.labels}))