Thanks my concern here is that I could end up double spending?
Meaning instead of sending x BTC to the intended address, I could end up sending 2x?
Is there a way to confirm (after doing it) that I have overwritten the old transaction?
Once done and it works
Do you control any of the receiving addresses (eg a change address) ? As you could spend the funds sent to that address at a higher rate but if electrum has already forgotten about the transaction it might be harder it set up (unless electrum says "+x btc unconfirmed".
How do I know whether I control a receiving address?
Also, what do you mean by "you could spend the funds sent to that address at a higher rate"?
Thanks!
Part of the reason bitcoin is a valuable digital currency is that you can't spend the same UTXOs twice. If there are two conflicting transactions that are trying to spend the same coins, only one of them will be included in a block. The other will get dropped and become invalid. Most likely the second transaction with a higher fee will be included first thereby making the lower fee transaction invalid. Please note, both transactions cannot be included in the same block either because it would make the whole block invalid and rejected by the network. Please also note, if you decide to do nothing about your transaction and leave it alone, if it is not confirmed after 14 days it will be dropped out of the mempool, which means you can construct another transaction with a higher fee.