I know there is a grand connection tree with every leaf representing a node, would it be at least theroetically possible for a tm to connect to any active node though it?

Possibly with an echo?

A TM that's already done a submergence can go back through the resonance realms without the need of a special echo, and can go through the great connection to another node on the matrix. The catch to this, IIRC, is that the TM must have a way to access this node without hacking it. The advantage is that your access is effectively untraceable by anyone save another TM. The drawback is that it can potentially take just as long as probing the target normally in the time it takes to pass through the event horizon (Unwired, page 174; Resonance + Fading Attribute + Submersion Grade (12, 1 hour) test).