The Town Council recently approved a measure that would make it easier for developers to build a seven-story hotel across Arsenal Street from the former Arsenal Mall retail complex. Councilors passed the zoning amendment Feb. 11 to allow hotels up to a height of 79 feet in the “Industrial 1’’ zoning district, an area mostly dominated by the mall, recently renamed the Arsenal Project, and a shopping plaza that includes Best Buy and Target, said planning director Steve Magoon. Previously, the ordinance allowed hotels to be built up to 50 feet, or five stories, tall, Magoon said. The new measure comes after Athenahealth Inc. and Boston developer Boylston Properties bought the Arsenal Mall and two nearby properties last summer. Boylston Properties has been lobbying for the change allowing a seven-story hotel on the former Charles River Saab site at 570 Arsenal St. for months. The developer has not submitted a formal application for the project, Magoon said, but he anticipates that the paperwork will be filed by this spring. Magoon said the development would likely be a midrange-quality hotel with limited services.