When dealing with templates, Pathfinder as a base only increases the CR of the creature the template is applied to. This would mean a PC would be able to gain a template with no problems considering a CR increase would not account for a Level Adjust. Since Pathfinder has no real rules for PCs gaining Templates I will make some.
When creating or adjusting a character with templates they are effectively put at an “experience debt” or “experience cost” this means they have to pay off this debt in order to continue leveling or immediately pay this experience total from their player xp. It doesn’t change their ECL or anything like that, they just gained extra power and as such had to pay for it with their experience. The way this will work is, for each CR bonus of the Template that is how many levels of experience you need to pay for. Start by calculating it as level 1 + the CR increase to determine the debt. For example a CR +3 would make the character “effectively” level 4 for this purpose and as such would give a PC a debt/cost of 6000 (fast scaling) this debt/cost works in a few ways.
- If the PC has “debt” they cannot gain more experience than the highest level character minus their debt (ex. If the highest level character has 10,000xp the CR + 3 character cannot go past 4,000xp) unless the PC uses some of their XP rewards to pay off their debt. This allows the player to choose between paying off their template or gaining a level. In certain cases where they gain extra xp they might want to put that towards their debt. It is also of note that a character with XP debt may not use the downtime system to gain xp.
- If the PC has the experience available if their current character “meets their end” they may buy a template for their next character. This subtracts the xp from the total before the character is created resulting in a templated creature of a possibly lower level than the previous character.
The templates usable in this manor are only inherited templates, acquired templates are something that must be done in game in order to attain them. And they come with a more flexible cost of 1/3rd the character level as the starting point + the CR/LA of the template.