How can I change observation states' values in OpenAI gym's cartpole environment?

I don't recommend changing the rules of the environment.

What you could do:

Perform a method called bucketing i.e. take a value from a continuous state space see which discrete bucket it should go into and then let your agent use the bucket number as the observation.

e.g. Say I do have a continuous state space with one variable in range $[-infty,infty]$

The buckets can be as follows:

0). x < -1000

1). -1000 $le$ x $<$ -500

2). -500 $le$ x $<$ -100

3). -100 $le$ x $<$ -50

4). -50 $le$ x $<$ 0

5). 0 $le$ x $<$ 50

6). 50 $le$ x $<$ 100

7). 100 $le$ x $<$ 500

8). 500 $le$ x $<$ 1000

9). x > 1000

Therefore in this example scenario there are 9 buckets. Hence, the observations can be in range [0, 9] discretely.