dzham @tim yep I'd recommend checking out the JS SDK. It allows you to construct transactions with whatever public key and sequence number you want. For example:
var public_key = "GDCHYXALGE4WCC35UPABVVXIJDHDSUKJTMLP4YA2LE3IBAF2PPC355BR";
var sequence_number = "100";
var account = new StellarSdk.Account(public_key, sequence_number);
var transaction = new StellarSdk.TransactionBuilder(account);
var operation = StellarSdk.Operation.payment({
destination: "GB2XS4IDKVGN63DZIDFXOCD7TGU43KLCLYF5JLL6WUPM6MMRNTWKTSPN",
asset: StellarSdk.Asset.native(),
amount: "10",
})
transaction.addOperation(operation);
transaction.build();