Having long since conquered SoMa and spread into Mid-Market, San Francisco’s high-octane technology boom is changing the face of another territory: the Financial District. Nondescript office towers that have traditionally provided 9-to-5 shelter to the city’s bankers, lawyers and insurance executives are increasingly filling up with app developers, coders and social media managers. Since 2010, the amount of space that tech companies occupy in San Francisco towers over 12 stories has jumped from 3.5 million square feet to 7.2 million square feet, according to the commercial real estate brokerage CBRE. Of the eight office buildings under construction in the city, 100 percent of the space has been preleased to technology companies. The tech invasion is accelerating the cultural shift in downtown San Francisco away from a formal suit-and-tie business environment, said Meade Boutwell, senior vice president at CBRE. Deloitte, a large consulting company, became the anchor tenant, and CNA Insurance also leased space. [...] a tech co-working group, WeWork, is negotiating a 100,000-square-foot lease in the building, according to real estate brokers familiar with the negotiations. Instead of adapting to traditional office layouts — with private offices, drop ceilings and big, formal conference rooms — tech companies are remaking these spaces. While getting a space near the windows in buildings like 535 Mission St.