NAT issue - urgent

[vallan]

I am in the process of setting up a Site to Site VPN with a remote client.

Usually we use our private ip address and then after the tunnel is through, remote users are able to ping through.

Now I have a new client who is unfortunately using the same private ip range as us.

My question is If I now add new public address to the node that only had an internal address , will it affect existing VPNs formed that has been using the private address?

e.g.

Node a = 172.16.14.1 and Node b = 172.16.14.2 these are the private addresses used with remote Client site to site VPN.

Now using the same Node a and Node b, I need to add public address to their NAT,

Node a = 172.16.14.1 also 90.172.12.1
Node b = 172.16.14.2 also 90.172.12.2

Will there be an issue?.

If there was going to be, how else can I achieve trying to set up VPN to another site which also have the same internal network as us?

Thanks