Can I just access the money in a lijfrente?

No. A lijfrente is fiscally locked until your retirement date. That is the trade-off for the deduction you receive on your contribution.

Exceptions are long-term incapacity for work and emigration. If you surrender it, the Dutch tax authority treats this as negative uitgaven voor inkomensvoorzieningen: you repay the amounts previously deducted and usually 20% revisierente as well. So only contribute what you can spare. Calculate your buffer.