This is the answer of greenadress support team
Hi,
As you may know, we recently announced some updates at https://blog.greenaddress.it/2017/09/06/segregated-witness-updates/ which includes backend support for signing bcash transactions. Please see the link for more details.
We provided this support in order to allow users to control their coins manually with respect to bcash. We are not however planning to support it in our wallets. We notified users of this as soon as possible after becoming aware of the bcash fork in order to allow users to move their coins if they wished to split themselves. Providing this support has already entailed considerable development and testing effort to ensure the safety and security of the services we provide. We are not able to provide technical support for splitting, transacting in or using bcash beyond the above.
Note that splitting coins is a technical process and the process may change depending on the development direction of bcash which like all contentious forks we neither support nor follow the development of. We have ensured as far as we are able that the service will not sign bcash transactions that can be replayed on the bitcoin main chain, this is the absolute limit of our support.
As you may be aware, a user at https://reddit.com/r/greenaddress has written a tool that allows splitting of bcash using a modified version of our garecovery tool which some people have reported success with. We have reviewed the code for bad intent and given the git commit hash of that reviewed version. If the tool is updated then we will similarly review the updated commits as and when we are able. We do not support the tool nor can make any guarantee on its quality. We will provide support in regards to the newly introduced api call https://api.greenaddress.it/vault.html#sign_alt_tx
Beyond this we offer no support whatsoever. It is each user's decision to use any third party tool and to ensure the security of their mnemonics etc while doing so. We are happy for users to discuss the tool and provide support for each other on the appropriate thread(s) on reddit subject to our normal moderation policy. This may change if the tool is changed to become malicious or the forum is spammed etc with bcash related topics or trolling.
Regards,
The GreenAddress support team