The trim is decorative, but the top trim on a tank this size will have a cross brace & that is structural.
You can however, make a cross brace out of glass. Look at the DIY forum for the DIY glass tank sticky & see how they make a glass brace. Basically, you get a 6" or so wide 1/4" glass that will fit exactly front to back & silicone that to the front & back glass in the middle at the top. This will prevent the tank from bowing out when fill & stressing the seams.
BTW, if you go to RONA or Canadian tires, you will find the store brand 100% clear silicone (for windows & doors - without mildrewcide or other additives - don't use the bathroom/kitchen ones) that will say "ideal for aquarium" on the tube. I got mine for less than $3.... much less than at a lfs
. This is FAIK
identical to GE silicone I in the US.
Going the DIY route, you should be able to repair the tank at well under $10.
If you have a really old tank, it might not have a center brace (like mine). These tanks have much thicker glass than the new ones (my 70 gal
has 3/8" glass vs 1/4" in a new tank ... you would see 1/2" in a 90). If you have one of these, you can fill it out & check for bowing. If the tank bows out less than 1/4" or so at the center when full, you won't need to add a brace. Warning, you do this outside ... check the glass as you are filling & stop as soon as any bowing is evident ... it is possible to bust a seam or crack the glass doing this test!!!