Replace Values Between Two Keywords In A Column?

I have data in which there are important keywords within a row (e.g.,# Message: FacesSc0_1) that are 'boundary markers' for data that is relevant to me. What I want to do is to select the data in the column between two such keywords, replace them all with the same specific value, and delete the other rows.

For example a column may look like this:

534.88
534.78
# Message: FacesSc0_1
534.78
534.55
534.59
# Message: FacesSc0_2
534.55
534.55
# Message: FacesSc0_3
534.78
534.55
534.59
# Message: FacesSc0_4

I would like to replace the values in the cells between "# Message: FacesSc0_1" and "# Message: FacesSc0_1" with the value 1, delete the values between "# Message: FacesSc0_2" and "# Message: FacesSc0_3", and replace the values in the cells between "# Message: FacesSc0_3" and "# Message: FacesSc0_4" with value 2. The resulting column would be reduced to this:

# Message: FacesSc0_1
1
1
1
# Message: FacesSc0_2
# Message: FacesSc0_3
2
2
2
# Message: FacesSc0_4