is it possible to choose which index you want to aim for when sending a transaction? Lets say there are 100 transactions all with 5 gwei, if i want to be on index 25, would it be possible to send the transaction and add a parameter to be placed on index 25?
I don't think it is possible, the transaction index is a computed value after the block is mined. the index is determined by how much gas you are paying for the transaction.
To be on the top you pay more but to be in the middle you need to pay more than the transaction lower than you and less than the one on top of you. the price you are paying is the product of gasPrice and gasAmount (gasPrice * gasAmount) so you will need to calculate it and push it with the needed values.