Can you ask for an extension of the visa "marriage" that you got in another country to become visa extension for having a child? No extension based on marry Thai has been given yet still under 3 month from entry

If you are married you cannot apply for an extension of stay based upon being the parent of a Thai, Those are only meant to be for a single parent.

You can only apply for an extension of stay based upon marriage.

The problem as you can see in the other thread I am in the middle of a divorce so i guess this is something I should do when the divorce is finished. What are the rules for this?

Once you are divorced and have at least joint custody of your child you can apply for the extension based upon being the parent of a Thai. You will need your divorce decree granting you custody when you apply for the extension.

As an interim solution you it would be best to get a multiple entry non-o visa in Savannakhet based upon marriage. If you could get you wife to sign/date a copy of her house book and ID card you could easily get it.