Upgrading from 1.6.12 that has major customization: Will I lose the tweaks?

[givenality]

Hello,

I've just read that 1.6 is coming to and end in 1st October, which forces me to upgrade to 1.8 ASAP. I have been very hesitant to upgrade to 1.8 because I have made a lot of customization from template to core system files in my forum and I fear I will lose a lot of them if I upgrade to new version. Will this be the case? If so, how much loss will I incur in terms of modifications made?

My site is: www.myelimu.com

Thank you in advance. Kind regards.

[.m.]

for changed source files you have to take backup of everything and customize again as required.
custom codes in templates are not wiped out by upgrading. yet, its better to backup the themes & use as required.