While it is not possible to lock positions in PowerPoint it is very easy to make an Office Theme that adjusts fonts and placeholder positions and sets colors for an entire presentation in a single click.
If you're not familiar with Themes (.thmx) files then I think you should take the time to learn about them. They may be just what you need.
To make an Office theme, in a new, blank presentation switch to Master Slide view. Set the page size and format the slide master's background. Go to the Format menu and choose Theme Colors. Set the colors as desired. Then, on the slide master use Command-A
to select all the elements at once and apply the font family you want.
If you want to add/remove/edit slide layouts, do that now.
When you're ready to save everything as a theme, click the Themes button on the Slide Master tab of the Ribbon and choose Save Current Theme.
Return to Normal View and your theme will now show up in the RIbbon when you click on Themes,
Distribute the .thmx file and save it in the same location on each workstation. When you want to enforce the theme simply apply it.
As a bonus, theme fonts and colors also become available in Word and Excel. When a Theme is applied in all Office apps the colors and fonts chosen apply to many ingredients such as charts, Excel tables, WordArt and SmartArt.