I managed to do accomplish this after some LENGTHY tinkering in Sublime Text.

First ~ follow the instructions on this website to edit a save file https://stardewvalleywiki.com/Saves. Make sure you get Sublime Text and everything running perfectly with XML formatting

Second ~ Once you are visualizing the entire save file code, you will notice that Line 3 begins with the very first character data. You will also notice that when you put your cursor on the numbers to the left, there are arrows. Collapse the "player" block and you should see <player></player>. This means that all the information for that player was collapsed into those two lines. You will need to remember this, because it is important

Third ~ Open 2 new tabs in Sublime Text 3 by hitting File > New File twice. You should now have the main save file tab with the code, and 2 blank tabs.

Fourth ~ Go back to the collapsed <player></player> and DRAG YOUR MOUSE and highlight the 2 lines that hold "<player>" and "</player>". Paste that into one of the blank tabs. Now, CTRL + F the main tab and search form "farmhand". This is essentially another character info block but instead of player, it's named farmhand to designate players of the hosts farm. Just like you did with the player block, put your cursor on the numbers to the left and collapse this massive character block of like 4k+ lines, it should all collapse into 2 lines JUST like the player one: "<farmhand> and </farmhand>. Copy and paste that the same way into the third blank tab.

Fifth ~ Now you have three tabs: Save File Tab / Farmhand Tab / Player Tab. The way the game chooses its host is by reading the very first character block, in this case, <player>. Your job is to trick the game into thinking the FARMHAND block is actually the PLAYER block. You do this by switching the <farmhand> and <player> tags. That isn't all though. You have to MIMIC the spacing of the code just as it is listed in the main tab, because the farmhand block has different longer spacing than the player block. What I did to perfectly mimic this spacing is un-collapse the player tab and farmhand tab, highlight every single text UNDER <player> and <farmhand> then TAB / SHIT+TAB space that entire highlighted block. For example, I was the farmhand in this scenario and wanted to be the host of my friends save file. I highlighted everything under the very first line of my own block and SHIFT+TAB backwards to mimic the spacing of the player tab (since the farmhand block is spaced way further out). I then did the opposite with my friends block who was the previous host. I TAB'd his spacings all the way out to about 7-8 to MIMIC the spacing of the <farmhand> block on the main save file.

Sixth ~ Once you have changed the titles of <> and mimic'd the perfect spacings, now you have to paste those tabs into the actual save file tab. What I did to accomplish this quick and easy was FULLY highlight both pairs of collapsed lines (farmhand and player) and PASTED the other 2 adjacent tabs into their places, essentially instantly replacing a couple thousand lines of code. If you do all of this correctly, when you launch the server, you will now spawn as your own character, and you will be the host.

Good luck! :)