According to our company policy, the warranty for this device will be terminated once it is modified by the user. It is recommended that you should not do any modification for this device.
If it is necessary to incorporate the external antenna to this device, here is a possible solution as stated by our engineers:
Based on the diagram, there is a circular RF test contact pin the back of the mother PCB. It will be the most suitable location to connect the external antenna. The center part of the circular contact pin is for connecting the signal line and the circumferential copper ring is for connecting the ground line both coming from the external antenna. Per this instructions, the external antenna would work. However, the GPS sensitivity would be not so good as tested by our RF engineers.
Let us know if you have any questions.