When I started with BASIC (urghhh) the system/editor had a facility that automatically renumbered to increments of 10. Of course, when a high school teacher then tried to introduce us to Pascal, my brain had already been tainted. Thankfully Uni enlightened me.
Back in <cough> I only had access to a disassembler built in to the Apple][ ROM and so inserting code was a nasty issue.
I basically started out with a machine code monitor as well. In fact the first one I used didn't even have support for mnemonics, you just had a hexdump of upcodes. In fairly short order (8-9 months) I got a monitor with mnemonic support, then progressed to Commodores slow as molassees two pass file based assembler and finally on to Turbo Assembler which had everything in RAM and was lightning fast.
cheers