Most people run a bunch of mono backing and then 100 or so yards of braid on their dipsy reels so no, you don't have to re-spool completely if you get a nick. Worst case you change the braid
I am one of those people..
20lb big game for backing to fill 85% of the spool then top it off with 100yrads of 30lbs braid.
Running up to 4dipsy diver rigs at any given time and the most I ever had to cut off was about the 10-20ft.. and that's only at the start of the season so I have a fresh "working" section of line and knot. 33trips on the lake last year and never had to replace or trim any more then the 20ft I cut off at the start of season.
If I do have to replace line it's only ever the 100yards of braid like you said.. which only happenes about every 4years.
after 2 years of use I'll strip the braid off and turn it around a put in back on.. fresh 200ft of braid that has never seen light.
•• My two cents on the subject of "dipsy diver guidance"••..
Use to calibrate all my reels but i Cant say i calibrate my reels any more but i do keep all my reels FILLED TO THE TOP OF THE SPOOL.. every reel I owned over the years is most accurate with a full spool. I assume the calibration of the counter would be set to reading line going out off a full spool.
My settings for dipsy divers 90% of the time are 0 & 1.5.
On 0 setting using #0 dipsy I figure 3:1 ratio and for #1 dipsy 2:1..with 30lbs braid.
That's just my way and not to say it's the only way or even a accurate way as for as that goes.. just rough figures I found useful over the years to get me to where I want to be running..
Of course many variables such as currants, water resistants, line diameter, speed and even bait used will alter my figures plus or minus a foot or 2 but the way I use dipsy divers this seems to be rather accurate within a couple ft.
75ft of line out pulling #0 dipsy set on 1 with a RRF puts me down 20ft trolling at a speed of 2.7mph. Pulling a colorado blade harness on the same set up runs it at 18ft. I run this set up over the rock reefs and humps in the shallows at nanticoke so I have a pretty good idea of where it swimming. You really need to know where your baits are fishing over there other wise your going to be tying on a new bait every time you hit bottom, Vary Sharp unforgiving rocks.
SO!.. 50% dive for every foot of line out for #1 dipsy(no ring). 30% for #0 dipsy(with ring).
No charts and I know it's all ball park figures & my own personal findings but it works for me the way i set them & send out.. on 30lb braid..at 2.5-3mph pulling a variety of baits.