Allow to remove soft body anchors, using pybullet.removeConstraint (untested).

Usage example:
anchors = []
anchors.append(p.createSoftBodyAnchor(clothId  ,0,-1,-1))
anchors.append(p.createSoftBodyAnchor(clothId ,3,boxId,-1, [0.5,-0.5,0]))
for a in anchors:
  p.removeConstraint(a)

examples/SharedMemory/PhysicsServerCommandProcessor.cpp

@@ -310,9 +310,16 @@ struct InteralUserConstraintData
 
 	b3UserConstraint m_userConstraintData;
 
+	int m_sbHandle;
+	int m_sbNodeIndex;
+	btScalar m_sbNodeMass;
+
 	InteralUserConstraintData()
 		: m_rbConstraint(0),
-		  m_mbConstraint(0)
+		  m_mbConstraint(0),
+		  m_sbHandle(-1),
+		  m_sbNodeIndex(-1),
+		  m_sbNodeMass(-1)
 	{
 	}
 };
@@ -11226,8 +11233,13 @@ bool PhysicsServerCommandProcessor::processCreateUserConstraintCommand(const str
 					if (bodyUniqueId<=0)
 					{
 						//fixed anchor (mass = 0)
+						InteralUserConstraintData userConstraintData;
+						userConstraintData.m_sbHandle = clientCmd.m_userConstraintArguments.m_parentBodyIndex;
+						userConstraintData.m_sbNodeIndex = nodeIndex;
+						userConstraintData.m_sbNodeMass = sbodyHandle->m_softBody->getMass(nodeIndex);
 						sbodyHandle->m_softBody->setMass(nodeIndex,0.0);
 						int uid = m_data->m_userConstraintUIDGenerator++;
+						m_data->m_userConstraints.insert(uid, userConstraintData);
 						serverCmd.m_userConstraintResultArgs.m_userConstraintUniqueId = uid;
 						serverCmd.m_type = CMD_USER_CONSTRAINT_COMPLETED;
 					} else
@@ -11278,6 +11290,10 @@ bool PhysicsServerCommandProcessor::processCreateUserConstraintCommand(const str
 						}
 						int uid = m_data->m_userConstraintUIDGenerator++;
 						serverCmd.m_userConstraintResultArgs.m_userConstraintUniqueId = uid;
+						InteralUserConstraintData userConstraintData;
+						userConstraintData.m_sbHandle = clientCmd.m_userConstraintArguments.m_parentBodyIndex;
+						userConstraintData.m_sbNodeIndex = nodeIndex;
+						m_data->m_userConstraints.insert(uid, userConstraintData);
 						serverCmd.m_type = CMD_USER_CONSTRAINT_COMPLETED;
 
 					}
@@ -11740,6 +11756,24 @@ bool PhysicsServerCommandProcessor::processCreateUserConstraintCommand(const str
 				delete userConstraintPtr->m_rbConstraint;
 				m_data->m_userConstraints.remove(userConstraintUidRemove);
 			}
+			if (userConstraintPtr->m_sbHandle >= 0)
+			{
+				InternalBodyHandle* sbodyHandle = m_data->m_bodyHandles.getHandle(clientCmd.m_userConstraintArguments.m_parentBodyIndex);
+				if (sbodyHandle)
+				{
+					if (sbodyHandle->m_softBody)
+					{
+						if (userConstraintPtr->m_sbNodeMass >= 0)
+						{
+							sbodyHandle->m_softBody->setMass(userConstraintPtr->m_sbNodeIndex, userConstraintPtr->m_sbNodeMass);
+						}
+						else
+						{
+							sbodyHandle->m_softBody->removeAnchor(userConstraintPtr->m_sbNodeIndex);
+						}
+					}
+				}
+			}
 			serverCmd.m_userConstraintResultArgs.m_userConstraintUniqueId = userConstraintUidRemove;
 			serverCmd.m_type = CMD_REMOVE_USER_CONSTRAINT_COMPLETED;
 		}

src/BulletSoftBody/btSoftBody.cpp

@@ -558,6 +558,25 @@ void btSoftBody::appendDeformableAnchor(int node, btRigidBody* body)
     m_deformableAnchors.push_back(c);
 }
 
+void btSoftBody::removeAnchor(int node)
+{
+	const btSoftBody::Node& n = m_nodes[node];
+	for (int i = 0; i < m_deformableAnchors.size(); )
+	{
+		const DeformableNodeRigidAnchor& c = m_deformableAnchors[i];
+		if (c.m_node == &n)
+		{
+			m_deformableAnchors.removeAtIndex(i);
+		}
+		else
+		{
+			i++;
+		}
+	}
+}
+
+
+
 //
 void btSoftBody::appendDeformableAnchor(int node, btMultiBodyLinkCollider* link)
 {

src/BulletSoftBody/btSoftBody.h

@@ -927,6 +927,7 @@ public:
     void appendAnchor(int node,
 					  btRigidBody* body, bool disableCollisionBetweenLinkedBodies = false, btScalar influence = 1);
 	void appendAnchor(int node, btRigidBody* body, const btVector3& localPivot, bool disableCollisionBetweenLinkedBodies = false, btScalar influence = 1);
+	void removeAnchor(int node);
 	/* Append linear joint													*/
 	void appendLinearJoint(const LJoint::Specs& specs, Cluster* body0, Body body1);
 	void appendLinearJoint(const LJoint::Specs& specs, Body body = Body());