Yes. You lose the PPOR exemption when you split off land so be prepared to pay on the full gain for the land sale.
To reduce the profit, you need to increase the purchase price, which is called the cost base for capital gains purposes. The higher it is, the lower the tax. To do this, you'll need to apportion the original purchase of the entire lot (both pieces of land and the building). You can add to the cost base by adding extra costs to the saleable land such as 50% of shared costs (eg stamp duty on purchase, subdivision application) and 100% of direct costs.
For example, you buy land and a house for $250,000. You live in the house. You split off the land at the back and the valuer tells you that the land was worth $100,000 when you purchased the property. You sell it for $200,000. You spent $12,000 on it in both shared expenses and direct expenses. Your gain is $88,000 which can be discounted to $44,000 if you owned it for more than a year, which is then taxed at your marginal rate.