I sent a transfer but the transaction is still in the transaction pool. Can I cancel it?
Edit: Not working from at least v0.15.0.4. I am getting the following error:
"Couldnt send the money: transaction was rejected by daemon with status: . Reason: double spend".
tl;dr: Reset wallet to make coins spendable again.
Quickest way to free up coins again, is just deleting the wallet .keys file. Then it will force resync, and then the coins are spendable again.
Though you will have two transactions in the mempool, the new transaction will make the older one unusable, once the new one is in a block.