Yes, if it is external, such as Party A, then no matter who is the first responsible person, if there is any breach of contract, the signatory shall bear the corresponding legal responsibilities according to the agreement. If it is internal, an agreement can be signed to stipulate the distribution of responsibilities between two people. This agreement is legal and valid.

In case of disputes in the future, the party with more responsibilities may demand compensation from the other party as agreed.

As far as the contract is concerned, there is nothing wrong with being cautious. The clearer and more detailed the regulations, the less likely it is to cause disputes. If both parties agree to a supplementary agreement, it is ok to sign another one.

Regarding signature and seal, we should correctly understand:

It is a common way for Chinese enterprises to conclude a contract in written form, such as a contract, which is signed and sealed by both parties. China's relevant laws and administrative regulations also have provisions on signature and seal.

For example, Article 10 of China's Technology Contract Law and Article 7 of China's Foreign-related Economic Contract Law stipulate that "a technology contract shall be established after being signed and sealed by the parties." The contract law has kept this effective way of signing written contracts in China's trade practice.